Gallium nitride containing laser device configured on a patterned substrate

ABSTRACT

A gallium and nitrogen containing laser diode device. The device has a gallium and nitrogen containing substrate material comprising a surface region. The surface region is configured on either a non-polar crystal orientation or a semi-polar crystal orientation. The device has a recessed region formed within a second region of the substrate material, the second region being between a first region and a third region. The recessed region is configured to block a plurality of defects from migrating from the first region to the third region. The device has an epitaxially formed gallium and nitrogen containing region formed overlying the third region. The epitaxially formed gallium and nitrogen containing region is substantially free from defects migrating from the first region and an active region formed overlying the third region.

This application is a continuation of U.S. patent application Ser. No.15/887,217, filed Feb. 2, 2018, which is a continuation of U.S. patentapplication Ser. No. 15/289,914, filed Oct. 10, 2016, which is acontinuation of U.S. patent application Ser. No. 14/857,719, filed onSep. 17, 2015, which is a continuation of U.S. patent application Ser.No. 14/317,846, filed on Jun. 27, 2014, which claims the benefit of U.S.Patent Application Ser. No. 61/841,138, filed on Jun. 28, 2013, each ofwhich are hereby incorporated by reference for all purposes. Thisapplication is related to U.S. application Ser. No. 13/651,291 filed onOct. 12, 2012, and U.S. application Ser. No. 13/850,187 filed on Mar.25, 2013, both of which are hereby incorporated by reference for allpurposes.

FIELD

The present disclosure relates to methods for users of electronicdevices to regulate their activities by helping them to balanceentertainment or communication activities with educational orproductivity activities. The disclosed methods monitor and control, forexample, the time kids spend on games and ensure that such time can bebalanced with use of educational applications.

BACKGROUND

The present disclosure relates generally to optical techniques. Morespecifically, the present disclosure provides methods and devices usingsemi-polar oriented gallium and nitrogen containing substrates foroptical applications.

In 1960, the laser was first demonstrated by Theodore H. Maiman atHughes Research Laboratories in Malibu. This laser utilized asolid-state flashlamp-pumped synthetic ruby crystal to produce red laserlight at 694 nm. By 1964, blue and green laser output was demonstratedby William Bridges at Hughes Aircraft utilizing a gas laser designcalled an Argon ion laser. The Ar-ion laser utilized a noble gas as theactive medium and produce laser light output in the UV, blue, and greenwavelengths including 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5 nm,488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ion laserhad the benefit of producing highly directional and focusable light witha narrow spectral output, but the wall plug efficiency was <0.1%, andthe size, weight, and cost of the lasers were undesirable as well.

As laser technology evolved, more efficient lamp pumped solid statelaser designs were developed for the red and infrared wavelengths, butthese technologies remained a challenge for blue and green and bluelasers. As a result, lamp pumped solid state lasers were developed inthe infrared, and the output wavelength was converted to the visibleusing specialty crystals with nonlinear optical properties. A green lamppumped solid state laser had 3 stages: electricity powers lamp, lampexcites gain crystal which lases at 1064 nm, 1064 nm goes into frequencyconversion crystal which converts to visible 532 nm. The resulting greenand blue lasers were called “lamped pumped solid state lasers withsecond harmonic generation” (LPSS with SHG) had wall plug efficiency ofabout 1%, and were more efficient than Ar-ion gas lasers, but were stilltoo inefficient, large, expensive, fragile for broad deployment outsideof specialty scientific and medical applications. Additionally, the gaincrystal used in the solid state lasers typically had energy storageproperties which made the lasers difficult to modulate at high speedswhich limited its broader deployment.

To improve the efficiency of these visible lasers, high power diode (orsemiconductor) lasers were utilized. These “diode pumped solid statelasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nmdiode laser, 808 nm excites gain crystal which lases at 1064 nm, 1064 nmgoes into frequency conversion crystal which converts to visible 532 nm.The DPSS laser technology extended the life and improved the wall plugefficiency of the LPSS lasers to 5% to 10%, and furthercommercialization ensue into more high end specialty industrial,medical, and scientific applications. However, the change to diodepumping increased the system cost and required precise temperaturecontrols, leaving the laser with substantial size, power consumptionwhile not addressing the energy storage properties which made the lasersdifficult to modulate at high speeds.

As high power laser diodes evolved and new specialty SHG crystals weredeveloped, it became possible to directly convert the output of theinfrared diode laser to produce blue and green laser light output. These“directly doubled diode lasers” or SHG diode lasers had 2 stages:electricity powers 1064 nm semiconductor laser, 1064 nm goes intofrequency conversion crystal, which converts to visible 532 nm greenlight. These lasers designs are meant to improve the efficiency, costand size compared to DPSS-SHG lasers, but the specialty diodes andcrystals required make this challenging today. Additionally, while thediode-SHG lasers have the benefit of being directly modulate-able, theysuffer from severe sensitivity to temperature, which limits theirapplication.

From the above, it is seen that techniques for improving optical devicesis highly desired.

SUMMARY

The present disclosure relates generally to optical techniques. Morespecifically, the present disclosure provides methods and devices usingsemi-polar oriented gallium and nitrogen containing substrates foroptical applications.

In an example, the present invention provides a gallium and nitrogencontaining laser diode device. The device has a gallium and nitrogencontaining substrate material comprising a surface region. The surfaceregion is configured on either a non-polar crystal orientation or asemi-polar crystal orientation. The device has a recessed region formedwithin a second region of the substrate material, the second regionbeing between a first region and a third region. The recessed region isconfigured to block a plurality of defects from migrating from the firstregion to the third region. The device has an epitaxially formed galliumand nitrogen containing region formed overlying the third region. Theepitaxially formed gallium and nitrogen containing region issubstantially free from defects migrating from the first region and anactive region formed overlying the third region.

In an example, the present invention provides a method for fabricating agallium and nitrogen containing laser diode device. The method includesproviding a gallium and nitrogen containing substrate materialcomprising a surface region, which is configured on either a non-polarcrystal orientation or a semi-polar crystal orientation. The methodincludes forming a migration blocking region (MBR) formed within asecond region of the substrate material. The second region is between afirst region and a third region. The MBR is configured to block aplurality of first defects from migrating from the first region to thethird region and is configured to block a plurality of second defectsmigrating from the third region to the first region. The method includesforming an epitaxially formed gallium and nitrogen containing regionoverlying at least the first region and the third region whilemaintaining the plurality of second defects in the third region andwhile maintaining the plurality of first defects in the first region andforming an active region formed overlying the third region.

In an alternative example, the present invention provides a gallium andnitrogen containing laser diode device. The device includes a galliumand nitrogen containing substrate material comprising a surface region,which is configured on either a non-polar crystal orientation or asemi-polar crystal orientation. The device has a migration blockingregion (MBR) formed within a second region of the substrate material.The second region is between a first region and a third region. The MBRis configured to block a plurality of first defects from migrating fromthe first region to the third region and is configured to block aplurality of second defects migrating from the third region to the firstregion. An epitaxially formed gallium and nitrogen containing region isformed overlying at least the first region and the third region whilemaintaining the plurality of second defects in the third region andwhile maintaining the plurality of first defects in the first region andforming an active region formed overlying the third region.

In an example, the present techniques include a transparent conductiveoxide such as indium tin oxide (ITO) incorporated in the p-type claddingregion or overlying the p-type cladding regions, highly reflectivemetals such as Ag overlying the p-type cladding regions, and/or etchedfacets. One or more examples of certain benefits that may be achievedwith this technique can be provided as follows:

1. Increased material gain due to higher material quality enablinghigher radiative efficiencies. Increased material gain will providelower threshold current density and higher laser efficiency.

2. Increased laser diode lifetime due to lower defect density in oraround the active region. Such defects can act as non-radiativecombination centers.

3. Increased strain budget to enable better active region and waveguidedesigns before the onset of strain induced material degradation. Forexample, this technique employed in a green laser design can enable thegrowth of high quality InGaN SCH layers with thicknesses ranging from 50nm to 150 nm with high indium content of up to 15% or higher InN molfraction. In other examples, this technique can enable green laserscontaining active regions with a very high number of quantum wells suchas 7, 9, 11, or even higher. Such design improvements allow for lowerloss and higher gain within the laser diodes to improve the efficiencyin preferred examples. These and other benefits can be achieved usingone or more of the following aspects:

1. Thin barriers ranging from 1.5 nm to 4 nm;

2. Substantially Al-free cladding regions;

3. 3-5 quantum wells, 6-8 quantum wells, 9-12 quantum wells;

4. Etched facets;

5. Transparent conductive oxide such as indium tin oxide (ITO) in oroverlying the p-type cladding regions;

5. Highly reflective metal contact such as Ag overlying the p-typecladding regions; and

6. Combinations of 4 and 5 and combinations of the other above.

In a first aspect, gallium and nitrogen containing laser diode devicesare provided, the devices comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the surface region beingconfigured on either a non-polar crystal orientation or a semi-polarcrystal orientation; a recessed region formed within a second region ofthe substrate material, the second region being between a first regionof the substrate and a third region of the substrate, the recessedregion being configured to block a plurality of defects from migratingfrom the first region to the third region; an epitaxially formed galliumand nitrogen containing region formed overlying the third region, theepitaxially formed gallium and nitrogen containing region beingsubstantially free from defects migrating from the first region; anactive region formed overlying the third region; a p-type regionoverlying the active region; a laser stripe region overlying a portionof the third region, the laser stripe region being characterized by acavity orientation substantially parallel to a projection of ac-direction or in a c-direction, the laser stripe region having a firstend and a second end; and a first facet provided on the first end of thelaser stripe region and a second facet provided on the second end of thelaser stripe region.

In a second aspect, gallium and nitrogen containing laser diode devicesare provided, the devices comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the substrate surfaceregion being configured on either a non-polar crystal orientation or asemi-polar crystal orientation; a migration blocking region (MBR) formedwithin a second region of the substrate surface region, the secondregion being between a first region of the substrate surface region anda third region of the substrate surface region, the MBR being configuredto block a plurality of defects from migrating from the first region tothe third region; an epitaxially formed gallium and nitrogen containingregion formed overlying the third region, the epitaxial region beingsubstantially free from defects migrating from the first region to thethird region; an active region formed overlying the third region; and ap-type region overlying the active region.

In a third aspect, methods for fabricating a gallium and nitrogencontaining laser diode devices are provided, the methods comprising:providing a gallium and nitrogen containing substrate materialcomprising a surface region, the substrate surface region beingconfigured on either a non-polar crystal orientation or a semi-polarcrystal orientation; forming a migration blocking region (MBR) within asecond region of the substrate surface region, the second region beingbetween a first region of the substrate surface region and a thirdregion of the substrate surface region, the MBR being configured toblock a plurality of first defects from migrating from the first regionto the third region and being configured to block a plurality of seconddefects migrating from the third region to the first region; forming anepitaxially gallium and nitrogen containing region overlying at leastthe first region and the third region while maintaining the plurality ofsecond defects in the third region and while maintaining the pluralityof first defects in the first region; forming an active region overlyingthe third region; and forming a p-type region overlying the activeregion.

In a fourth aspect, gallium and nitrogen containing laser diode devicesare provided, the devices comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the substrate surfaceregion being configured on either a non-polar crystal orientation or asemi-polar crystal orientation; a migration blocking region (MBR) formedwithin a second region of the substrate surface region, the secondregion being between a first region of the substrate surface region anda third region substrate surface region, the MBR being configured toblock a plurality of defects from migrating from the first region to thethird region and being configured to block a plurality of second defectsfrom migrating from the third region to the first region; an epitaxiallyformed gallium and nitrogen containing region formed overlying the thirdregion, the epitaxially formed gallium and nitrogen containing regionbeing substantially free from defects migrating from the first region;an n-type cladding region formed overlying the epitaxially formedgallium and nitrogen containing region; an active region formedoverlying the third region, the active region comprises a plurality ofquantum wells ranging from two to eleven, each pair of quantum wellregions having a barrier region disposed there between; a p-type galliumand nitrogen containing cladding region formed overlying the activeregion; and a laser stripe region overlying a portion of the thirdregion, the laser stripe region being characterized by a cavityorientation substantially parallel to a projection of a c-direction orin a c-direction, the laser stripe region having a first end and asecond end; a first facet provided on the first end of the laser striperegion and a second facet provided on the second end of the laser striperegion.

In a fifth aspect, gallium and nitrogen containing laser diode devicesare provided, the devices comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the substrate surfaceregion being configured on either a non-polar crystal orientation or asemi-polar crystal orientation; a migration blocking region (MBR) formedwithin a second region of the substrate surface region, the secondregion being between a first region of the substrate surface region anda third region of the substrate surface region, the MBR being configuredto block a plurality of defects from migrating from the first region tothe third region and being configured to block a plurality of seconddefects from migrating from the third region to the first region; anepitaxially formed gallium and nitrogen containing region formedoverlying the third region, the epitaxially formed gallium and nitrogencontaining region being substantially free from defects migrating fromthe first region; an n-type cladding region formed overlying theepitaxially formed gallium and nitrogen containing region; an activeregion formed overlying the third region, the active region comprising aplurality of quantum wells ranging from two to eleven, a barrier regiondisposed between each pair of quantum wells; a laser stripe regionoverlying a portion of the third region, the laser stripe region beingcharacterized by a cavity orientation substantially parallel to aprojection of a c-direction or in a c-direction, the laser stripe regionhaving a first end and a second end; a first etched facet provided onthe first end of the laser stripe region and a second etched facetprovided on the second end of the laser stripe region; and a p-typegallium and nitrogen containing cladding region formed overlying theactive region.

In a sixth aspect, gallium and nitrogen containing laser diode devicesare provided, the devices comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the substrate surfaceregion being configured on either a non-polar crystal orientation or asemi-polar crystal orientation; a migration blocking region (MBR) formedwithin a second region of the substrate surface region, the secondregion being between a first region of the substrate surface region anda third region of the substrate surface region, the MBR being configuredto block a plurality of defects from migrating from the first region tothe third region and being configured to block a plurality of seconddefects from migrating from the third region to the first region; anepitaxially formed gallium and nitrogen containing region formedoverlying the third region, the epitaxially formed gallium and nitrogencontaining region being substantially free from defects migrating fromthe first region; an n-type cladding region formed overlying the galliumand nitrogen containing region; an active region formed overlying thethird region, the active region comprises a plurality of quantum wellsranging from two to eleven, a barrier region disposed between each pairof quantum wells; a laser stripe region overlying a portion of the thirdregion, the laser stripe region being characterized by a cavityorientation substantially parallel to a projection of a c-direction orin a c-direction, the laser stripe region having a first end and asecond end; a first facet provided on the first end of the laser striperegion and a second facet provided on the second end of the laser striperegion; a p-type gallium and nitrogen containing cladding region formedoverlying the active region; and a conductive oxide layer overlying thep-type gallium and nitrogen containing cladding region.

In a seventh aspect, gallium and nitrogen containing laser diode devicesare provided, the devices comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the substrate surfaceregion being configured on either a non-polar crystal orientation or asemi-polar crystal orientation; a migration blocking region (MBR) formedwithin a second region of the substrate surface region, the secondregion being between a first region of the substrate surface region anda third region of the substrate surface region, the MBR being configuredto block a plurality of defects from migrating from the first region tothe third region and being configured to block a plurality of seconddefects from migrating from the third region to the first region; anepitaxially formed gallium and nitrogen containing region formedoverlying the third region, the epitaxially formed gallium and nitrogencontaining region being substantially free from defects migrating fromthe first region; an n-type cladding region formed overlying the galliumand nitrogen containing region; an active region formed overlying thethird region, the active region comprises a plurality of quantum wellsranging from two to eleven, a barrier layer disposed between each pairof quantum wells; a laser stripe region overlying a portion of the thirdregion, the laser stripe region being characterized by a cavityorientation substantially parallel to a projection of a c-direction orin a c-direction, the laser stripe region having a first end and asecond end; a first facet provided on the first end of the laser striperegion and a second facet provided on the second end of the laser striperegion; a p-type gallium and nitrogen containing cladding region formedoverlying the active region; a reflective metal layer overlying thep-type gallium and nitrogen containing cladding region; and thereflective metal layer comprises silver.

In an eighth aspect, gallium and nitrogen containing laser diode devicesare provided, the devices comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the surface region beingconfigured on either a non-polar crystal orientation or a semi-polarcrystal orientation; an epitaxially formed gallium and nitrogencontaining region formed overlying the substrate material; an n-typecladding region formed overlying the gallium and nitrogen containingregion; an active region formed overlying the third region, the activeregion comprising a plurality of quantum wells ranging from two toeleven, a barrier region disposed between each pair of quantum wells; alaser stripe region overlying a portion of the third region, the laserstripe region being characterized by a cavity orientation substantiallyparallel to a projection of a c-direction or in a c-direction, the laserstripe region having a first end and a second end; a first etched facetprovided on the first end of the laser stripe region and a second etchedfacet provided on the second end of the laser stripe region; a p-typegallium and nitrogen containing cladding region formed overlying theactive region; a reflective metal layer overlying the p-type gallium andnitrogen containing cladding region; and the reflective metal layercomprises silver.

In a ninth aspect, gallium and nitrogen containing laser diode devicesare provided, the devices comprising: a gallium and nitrogen containingsubstrate material comprising a surface region, the substrate surfaceregion being configured on either a non-polar crystal orientation or asemi-polar crystal orientation; an epitaxially formed gallium andnitrogen containing region formed overlying the substrate surfaceregion; an n-type cladding region formed overlying the epitaxiallyformed gallium and nitrogen containing region; an active region formedoverlying the third region, the active region comprises a plurality ofquantum wells ranging from two to eleven, a barrier region disposedbetween each pair of quantum wells; a laser stripe region overlying aportion of the third region, the laser stripe region being characterizedby a cavity orientation substantially parallel to a projection of ac-direction or in a c-direction, the laser stripe region having a firstend and a second end; a first etched facet provided on the first end ofthe laser stripe region and a second etched facet provided on the secondend of the laser stripe region; a p-type gallium and nitrogen containingcladding region formed overlying the active region; and a conductiveoxide layer overlying the p-type gallium and nitrogen containingcladding region.

Embodiments provided by the present disclosure achieve these benefitsand others in the context of known process technology. However, afurther understanding of the nature and advantages of the embodimentsdisclosed herein may be realized by reference to the specification andthe attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 illustrate schematics of basal and non-basal plane slipgeometries according to examples.

FIG. 3A shows emissions pertaining to formation of basal plane misfitsin or near the active regions in our green LD devices, grown on (20-21)oriented substrates according to examples.

FIG. 3B shows a microfluorescence image of basal plane and non-basalplane misfit in a (20-21) device.

FIG. 4A shows an image of a green laser diode having a (20-21)orientation with a high density of dark triangle defects.

FIG. 4B shows Nomarski mages of individual triangle defects with highermagnification image showing internal structure and point of nucleation.

FIG. 5A shows schematic diagrams of misfit distributions on substrateswith linear misfit blocking features arresting the glide of threadingdislocations in strained epitaxial films (e.g., the active region),according to certain embodiments.

FIG. 5B shows schematic diagrams of misfit distributions on substrateswithout misfit blocking features.

FIG. 6 shows a second defect type observed in our green devicesaccording to an example.

FIG. 7A shows the relationship between threading dislocation density andlinear misfit density for basal plane misfits.

FIG. 7B shows the calculated relationship between linear misfit densityand threading dislocation density on TDD for various average misfitglide lengths.

FIGS. 8A and 8B show etched mesas and etched trenches, respectively,that have been etched into the substrate prior to growth of epitaxiallayers.

FIG. 8C shows a trench produced with a selective area growth processutilizing a mask deposited on the wafer prior to growth of epitaxiallayers.

FIG. 8D shows a misfit barrier blocking feature defined by patterneddamage to a substrate consisting of defective GaN that is induced bysome pre-growth, patterned processing of the substrate wafer that thenyields defective regions in the subsequently grown epitaxial filmsaccording to certain embodiments.

FIGS. 9A and 9B show two types of blocking. FIG. 9A shows a monolithicapproach in which the etched trench or mesa coincides with the locationof a laser stripe, and the blocking occurs at the edges of this region.FIG. 9B shows an approach in which blocking features are separate orremote from the laser stripe, i.e. two or more trenches, mesas ordefective regions are defined on the substrate and the laser stripe isdisposed in a region between the blocking features according to certainembodiments.

FIG. 10 illustrates blocking features for control of threadingdislocation density in intentionally relaxed films according to certainembodiments. Typically one would expect misfits to glide an averagedistance, simply displacing the location of the original threadingdislocation and leaving the threading dislocation density anddistribution relatively unchanged. By introducing blocking features, oneforces the misfits to stop gliding at specific locations, therebyreducing the dislocation density within the device. Blocking featuregeometry can be tailored to either prevent misfit propagation onto laserdevice or encourage partial relaxation of epi-film via misfit formationwhile eliminating TDs.

FIG. 11A-11C show fluorescence micrographs of a laser diode structuregrown on a GaN semipolar substrate etched before growth with testpatterns consisting of 5 micron wide trenches separated by unetchedregions of varying width according to certain embodiments.

FIG. 12 shows a plot of linear density of striations measured at variouslocations on the test structures shown in FIG. 11 for different mesawidths according to certain embodiments.

FIG. 13 shows fluorescence micrographs of test structures consisting ofvarious trench widths and mesa widths according to certain embodiments.

FIG. 14A-14B shows micrographs of substrates with topological featuresetched into the sample surface illustrating the prevention of extendeddefects and other than misfits according to certain embodiments.

FIGS. 15A-15C show diagrams of the coalescence process for a narrowtrench, with trench width and depth selected to allow for coalescenceonly after the strained layers are grown according to certainembodiments.

FIG. 16A-16B shows laser diode films grown on patterned semipolarsubstrates containing regions isolated by 5 micron wide trenchesaccording to certain embodiments.

FIGS. 17A and 17B show spatial maps of photoluminescence measurementstaken from a single laser diode device grown on patterned a semipolarwafer according to certain embodiments.

FIG. 18 is a simplified schematic diagram of a semipolar laser diodewith a cavity aligned in the projection of c-direction with cleaved oretched facets according to certain embodiments.

FIG. 19 is a simplified schematic cross-sectional diagram illustrating alaser diode structure according to certain embodiments.

FIG. 20 shows a cross-sectional schematic of a gallium and nitrogencontaining laser diode with a first, second, and third region, where thesecond region is a migration blocking region and the third regioncontains the laser stripe region.

FIG. 21 shows a cross-sectional schematic of a gallium and nitrogencontaining laser diode with a first, second, and third region, where thesecond region is the migration blocking region and the third regioncontains the laser stripe region. In this configuration there are twomigration blocking regions protecting the third region from defectsformed in the first region.

FIG. 22 shows a cross-sectional schematic of a gallium and nitrogencontaining laser diode with a first, second, and third region, where thesecond region is the migration blocking region and the third regioncontains the laser stripe region. A reflective metal layer such as Ag ora conductive oxide such as ITO is positioned above the p-type claddingregion to reduce the modal overlap with the metal layer and hence reducethe loss. In this configuration the reflective metal or conductive oxideis configured only substantially above the ridge.

FIG. 23 shows a cross-sectional schematic of a gallium and nitrogencontaining laser diode with a first, second, and third region, where thesecond region is the migration blocking region and the third regioncontains the laser stripe region. A reflective metal layer such as Ag ora conductive oxide such as ITO is positioned above the p-type claddingregion to reduce the modal overlap with the metal layer and hence reducethe loss. In this configuration the reflective metal or conductive oxideis configured both above the ridge and above the dielectric materialadjacent to the ridge, making the deposition process similar to what maybe used to deposit the p-metal, such as a lift-off technique.

FIG. 24 is a simulation showing loss versus wavelength for a green laserdiode epitaxial structure grown on a semipolar gallium and nitrogencontaining substrate. The different curves represent different materialsdeposited between the p-cladding region and a standard metal contactlayer such as gold, along with only air above the p-cladding. As isshown, for a typical metal such as Titanium (Ti) the loss is about 8cm⁻¹ to 9 cm⁻¹, but can be reduced to 5 cm⁻¹ to 6 cm⁻¹ with the use of aconductive oxide like ITO and all the way down to 4 cm⁻¹ to 4.5 cm⁻¹ byusing a highly reflective metal layer such as silver (Ag). The loss isbeing reduced due to the reduced modal overlap with the metal layerabove these conductive oxide layers and reflective metal layers.According to the simulation, silver can provide a loss nearly identicalto that of having only air above the p-cladding, which is the idealcase.

DETAILED DESCRIPTION

The present disclosure relates generally to optical techniques. Morespecifically, the present disclosure provides methods and devices usingsemi-polar oriented gallium and nitrogen containing substrates foroptical applications. More particularly, the present invention providesa method and device using a gallium and nitrogen containing substrateconfigured on the {20-21} family of planes or an off-cut of the {20-21}family of planes toward the plus or minus c-plane and/or toward thea-plane according to one or more embodiments, but there can be otherconfigurations. Such family of planes include, but are not limited to,(30-3-2), (20-2-1), (30-3-1), (30-32), (20-21), (30-31) or anyorientation within +/−10 degrees toward c-plane and/or a-plane fromthese orientations. In particular, the present invention provides amethod and device for emitting electromagnetic radiation using nonpolaror semipolar gallium containing substrates such as GaN, AlN, InN, InGaN,AlGaN, and AlInGaN, and others. The invention can be applied to opticaldevices, lasers, light emitting diodes, solar cells,photoelectrochemical water splitting and hydrogen generation,photodetectors, integrated circuits, and transistors.

One feature of non-polar and semi-polar films is the formation of misfitdislocations at strained interfaces. In c-plane oriented films theavailable slip systems require sufficiently large strains to induce slipthat misfits are difficult to produce. This is not the case insemi-polar films, as slip of threading dislocations on the inclinedbasal plane and on inclined m-planes is commonly observed. It shouldalso be possible to see slip on prismatic planes and inclined a-planesin semi-polar and non-polar films. Indeed, slip on inclined m-planes isobserved at low density in some of our non-polar blue LD structures.

These misfits appear to form due to the translation of threadingdislocations that are inherent to the underlying GaN substrate. Thistranslation is driven by strain in the heteroepitaxial layer and leavesbehind a dislocation in the plane of the interface which relieves strainand is called a ‘misfit’ dislocation. See FIGS. 1 and 2 for schematicsof basal and non-basal plane slip geometries. In FIG. 2, angle of misfitθ relative to {1120} goes to 90° as substrate misorientation from (1010)goes to 0°. Formation of basal plane misfits in or near the activeregions is common in our green LD devices, grown on (20-21) orientedsubstrates, and impacts the emission from the active region as can beobserved in FIGS. 3A-3B. This may have a negative impact on our LDdevices, either by reducing radiative emission near the misfit, or bypopulating the laser stripe with localized regions of lower carrierconcentration due to higher non-radiative recombination rates near themisfits. Being able to prevent misfit formation in the region of asemipolar laser diode may enable higher performance for standardstructures as well as allow for the growth of fully strained structureswith much higher active region volumes (resulting in better AlGaN freeguiding as well as high current radiative efficiency) that are possiblewith high efficacy today.

FIG. 7B shows a rough calculation of misfit linear density vs. threadingdislocation density and average line length of a misfit. Thiscalculation assumes all threading dislocations participate in misfitformation. For substrates with high densities of threading dislocations(>1E6/cm²) the misfit density is large (>100/cm²) for even short averagemisfit lengths (˜1 micron). As the misfit line length approaches 1 mm,misfit densities can be kept below 100 cm² only by reducing thesubstrate TDD<1E2/cm². Misfit blocking structures may be necessary toprovide misfit free regions even on very high quality GaN substrates.

FIGS. 5A-5B shows a schematic of the general idea, with in FIG. 5A somegeneric linear blocking feature arresting the glide of threadingdislocations in the strained epitaxial films (e.g., the active region ofour devices), in an example. For non-polar films the blocking featuresmay be arrayed parallel to the c-plane so as to stop m-plane slip whichis sometimes observed in our non-polar blue devices. In semipolar films,both the basal and non-basal plane slip systems are oriented with somecomponent parallel to [0001], so [0001] parallel blocking features canbe used to limit their extent.

FIGS. 4A-4B and 6 describe a second defect type observed in our greendevices. These defects consist of degraded active region material andconsist of partially hollow or metal filled voids that are arrayed alongcrystallographic directions (giving the arrays of voids a triangularshape). Since these defects nucleate as a single point and then becomeself-propagating it may follow that we may be able to interrupt theexpansion of this kind of defect by introducing a discontinuity in theactive region.

The blocking features under consideration are shown in FIG. 8 andconsist of 4 classes of features. FIGS. 8A and 8B show mesas andtrenches, respectively, etched into the substrate prior to growth.Growth of the epitaxial layers do not fill the trenches and there iseither a step up or down at the edges of the features that can block theglide of threading dislocations. FIG. 8C shows a trench produced with aselective area growth process utilizing a mask deposited on the waferprior to growth. FIG. 8D shows the last class of blocking features,which may consist of defective GaN that is induced by some pre-growth,patterned processing of the substrate wafer that then yields defectiveregions in the subsequently grown epitaxial films. The defects in thedefective regions may then impede the motion of gliding threadingdislocations (e.g., similar to dislocation motion impediment at grainboundaries). This processing can consist of high-dose ion implantationof the substrate, deposition of an anti-surfactant, deposition ofnon-fully dense mask (e.g., micro-masking), deposition of a porous mask(e.g., nano-masking), deposition of foreign species to disturb growth(e.g., metals, silicon, anti-surfactants), or chemical or photo-chemicaletching of the substrate to produce porous GaN.

FIGS. 9A-9B shows the 2 classes of blocking that may occur. 9A shows amonolithic approach, where the etched trench or mesa is also thelocation of the laser stripe, and the blocking occurs at the edges ofthis region. FIG. 9B shows the other class, where the blocking featuresare remote from the laser stripe, i.e. two or more mesa or stripes (ordefective regions as in FIG. 8D) are defined on the substrate and thelaser stripe is disposed in a region between the blocking features.

FIG. 10 shows a potential application of such features that has not beenapplied to semipolar GaN substrates. Typically we expect to seethreading dislocations distributed more-or-less uniformly across oursubstrates. Depending on how the substrates are grown there may be somevariation from region to region across the wafer. The expectation is,especially for wider stripes, that some threading dislocations may befound in all stripe regions. Since threading dislocations are sources offailure in LDs, it may be advantageous to remove threading dislocationsfrom the regions where laser stripes will be defined. Typically, one mayexpect the glide of threading dislocations during misfit formation tomove all threading dislocations available to glide an average distance,leaving the threading dislocation distribution over the majority of thesubstrate unchanged. By introducing blocking features at some criticallength scale much shorter than the average misfit glide length one cantheoretically force a substantial portion or all of the threadingdislocations to collect at the blocking feature; leaving the region ofthe stripe relatively free of misfits. For certain designs, this canresult in partially relaxed (metamorphic) buffer layers that arerelatively threading dislocation free. Relaxation of the buffer layermay allow for growth of higher quality active regions due to the InGaNquantum wells being under lower strain. Because all of the misfits havebeen localized to the blocking features one can then growth even morehighly strained films on top of these relaxed buffers, as there may be amuch lower density of threading dislocations available to glide andresult in strain relaxation via misfit formation.

FIGS. 11A-11C shows fluorescence micrographs of a laser diode structuregrown on a GaN semipolar substrate etched before growth with testpatterns consisting of 5 micron wide trenches separated by unetchedregions of varying width. Parallel lines of contrast (referred to hereas “striations”) can be seen running perpendicular to the [0001]direction. These striations are due to spatial variation in radiativerecombination efficiency near misfit dislocations that form fromthreading dislocations that slip on the basal plane. Here it is shownthat the more narrowly spaced trenches bound regions significantly lowerstriation density than more widely spaced trenches. This is consistentwith the model that the misfit dislocations are derived from threadingdislocations inherent to the substrate, that the threading dislocationsslip due to misfit strain and propagate laterally through the film.Interrupting the areal contiguity of the strained layer through whichthe misfit is gliding with an etched feature, such as a trench or mesa,arrests the motion of the misfit. This limits the misfit density to be afunction of the total number of threading dislocation contained withinthe bounded region.

FIG. 12 shows a plot of linear density of striations measured at variouslocations on the test structures shown in FIG. 1. Striation densityvaries linearly with the width of the mesa. This is in agreement withthe hypothesis that basal plane misfits are derived from threadingdislocations inherent to the substrate, which are found with some finiteareal density. The optimal mesa width is then bounded at a maximum bythe desired misfit density and the substrate threading dislocationdensity and at a minimum the processing limitations of subsequent devicefabrication.

FIG. 13 shows matrix of fluorescence micrographs of test structuresconsisting of various trench widths and mesa widths. Images were takenfrom the same wafer. FIG. 13 shows that misfit density [as evidenced bydensity of striations in fluorescence micrograph contrast] depends onlyon mesa width and not trench width. i.e. a trench need only be wideenough to provide a disruption in the strained layer to be effective atstopping misfits.

FIGS. 14A-14B shows topological features etched into the sample surfacecan prevent propagation of extended defects other than misfits. FIG. 14Ashows etched trenches bisected by a defect in the original substratebefore patterning (most likely a scratch). The defect acts as anucleation site for misfit dislocations (extrinsic misfits, which arenot related to threading dislocations inherent to the substrate) whichcan be seen as striations in the contrast of the fluorescencemicrograph. Here the trenches are seen to be effective in preventing thepropagation of the induced misfits and limiting the impact of substratesurface defects. In FIG. 14B very narrow trenches (approximately 5microns wide) are shown to stop propagation of extrinsic misfits inducedby a “dark triangle” defect which is caused by degradation of InGaNcontaining layers. In the upper left hand corner of FIG. 14B it can beseen that trenches also prevent the expansion of dark triangle defects.Therefore it is shown that interrupting the lateral contiguity ofstrained and InGaN containing layers can stop propagation of a varietyof extended defects and limit their impact on device performance andyield.

FIGS. 15A-15C show that narrow trenches offer an advantages over mesasin that they: leave a more planar surface, require less area of thewafer to be etched, can be coalesced after growth of the strained layersto leave a planar surface that is more easily processed. FIGS. 15A-15Cshow diagrams of the coalescence process of a narrow trench, with trenchwidth and depth chosen to allow for coalescence only after the strainedlayers are grown.

FIGS. 16A-16B shows laser diode films grown on patterned semipolarsubstrates containing regions isolated by 5 micron wide trenches. InFIG. 16A, (1) and (2) show, respectively, Nomarski and fluorescencemicrographs of a wafer with trenches spaced at 20 micrometers. In FIG.16B, (1) and (2) show, respectively, Nomarski and fluorescencemicrographs of a wafer with trenches spaced at 20 micron regionbracketed by two sets of 3 trenches of the same dimensions as in FIG.16A. Thick regrowth on single trenches closely spaced led to reductionof misfit density as well as roughening of the surface between thetrenches. Thick regrowth on the structure in FIG. 16B isolated theroughening to the outermost sets of trenches while also reducing misfitdensity at the center of the pattern. In both cases the thickness ofgrown films was high enough to fill in the trenches. Note that images inB are taken at same location and magnification while images in A aresame location but original images were different magnifications.

FIGS. 17A-17B shows spatial maps of photoluminescence measurements takenfrom an epitaxial structure suitable for fabrication of green laserdiodes grown on a patterned semipolar wafer according to one embodimentof this technique using trench regions as the MBR is grown on the wafer.FIG. 17A shows peak spectral intensity [reported in Volts fromphotodetector], and FIG. 17B shows spectral full width at half maximum.Dotted lines indicate location of line scan shown in inset. Verticalregions are areas where wafers were patterned with trenches and theaverage misfit density is reduced relative to the unpatterned regions.As can be seen in the figure, the regions employing the MBR regionsexhibit higher photoluminescence intensity and narrower full width athalf maximum. The higher intensity is indicative of higher radiativerecombination and efficiency and the narrower full width at half maximumis indicative of more homogenous material, both of which indicate a muchimproved material quality. Such an improvement in material quality willenable a higher efficiency laser diode.

Forming laser diodes on semipolar orientations of gallium and nitrogencontaining material (e.g., GaN) can be advantageous. Such lasers mayinclude long wavelength emission, high gain properties, improvedmaterial quality, and/or increased design flexibility over alternativeplanes such as the conventional polar c-plane or even the nonpolarm-plane or polar c-plane. For example, we have fabricated true greenlaser diodes on the (20-21) semipolar plane and found that the (30-3-1)semipolar plane offers narrower full width at half-maximum (FWHM)emission spectra and higher gain compared to the nonpolar m-plane in theblue regime, as described in U.S. application Ser. No. 12/883,093 filedon Sep. 15, 2010, which is incorporated by reference.

As an example, FIG. 18 is a simplified schematic diagram of semipolarlaser diode with the cavity aligned in the projection of c-directionwith cleaved or etched mirrors. Example of projection of c-directionoriented laser diode stripe on semipolar (30-3-1) substrate with cleavedor etched mirrors. This diagram is merely an example, which should notunduly limit the scope of the claims herein. One of ordinary skill inthe art may recognize other variations, modifications, and alternatives.As shown, the optical device includes a gallium nitride substrate memberhaving a semipolar crystalline surface region characterized by anorientation of about 9 degrees to about 12.5 degrees toward (000-1) fromthe m-plane). In an embodiment, the gallium nitride substrate member isa bulk GaN substrate characterized by having a semipolar crystallinesurface region, but can be others. In an embodiment, the bulk GaNsubstrate has a surface dislocation density below 10⁵ cm⁻² or 10⁵ to 10⁷cm⁻². It should be noted that homoepitaxial growth on bulk GaN isgenerally better than hetero-epitaxy growth. The nitride crystal orwafer may comprise Al_(x)In_(y)Ga_(1-x-y)N, where 0≤x, y, x+y≤1. In anembodiment, the nitride crystal comprises GaN. In one or moreembodiments, the GaN substrate has threading dislocations, at aconcentration between about 10⁵ cm⁻² and about 10⁸ cm⁻², in a directionthat is substantially orthogonal or oblique with respect to the surface.As a consequence of the orthogonal or oblique orientation of thedislocations, the surface dislocation density is below about 10⁵ cm⁻² orbelow about 10⁷ cm⁻² others such as those ranging from about 10⁵ cm⁻²10⁸ cm⁻². In alternative example, is a projection of the c-directionoriented laser diode stripe on semipolar (20-21) substrate with cleavedor etched mirrors. The optical device includes a gallium nitridesubstrate member having a semipolar crystalline surface regioncharacterized by an orientation of about 13 degrees to about 17 degreestoward (0001) from the m-plane). In an embodiment, the gallium nitridesubstrate member is a bulk GaN substrate characterized by having asemipolar crystalline surface region, but can be others. In anembodiment, the bulk GaN substrate has a surface dislocation densitybelow 10⁵ cm⁻² or from 10⁵ cm⁻² to 10⁷ cm⁻².

In an embodiment, the device has a laser stripe region formed overlyinga portion of the semipolar crystalline orientation surface region. In anembodiment, the laser stripe region is characterized by a cavityorientation that is substantially parallel to the projection of thec-direction. In an embodiment, the laser stripe region has a first endand a second end.

In an embodiment, the device has a first facet provided on the first endof the laser stripe region and a second facet provided on the second endof the laser stripe region. In one or more embodiments, the first facetis substantially parallel with the second facet. Mirror surfaces areformed on each of the surfaces. The first facet comprises a first mirrorsurface. In an embodiment, the first mirror surface is provided by ascribing and breaking process or alternatively by etching techniquesusing etching technologies such as reactive ion etching (RIE),inductively coupled plasma etching (ICP), or chemical assisted ion beametching (CAIBE), or other method. Any suitable scribing process can beused, such as a diamond scribe or laser scribe or combinations. In anembodiment, the first mirror surface comprises a reflective coating. Inan embodiment, the reflective coating can be deposited using, forexample, e-beam evaporation, thermal evaporation, RF sputtering, DCsputtering, ECR sputtering, ion beam deposition, Ion AssistedDeposition, reactive ion plating, any combinations, and the like. Instill other embodiments, surface passivation may be used to the exposedsurface prior to coating. The reflective coating is selected fromsilicon dioxide, hafnia, and titania, tantalum pentoxide, zirconia,including combinations, and the like. Preferably, the reflective coatingis highly reflective and includes a coating of silicon dioxide andtantalum pentoxide, which has been deposited using electron beamdeposition. Depending upon the embodiment, the first mirror surface canalso comprise an anti-reflective coating. Additionally, the facets canbe cleaved or etched or a combination of them.

Also in an embodiment, the second facet comprises a second mirrorsurface. The second mirror surface is provided by a scribing andbreaking process according to an embodiment or alternatively by etchingtechniques using etching technologies such as reactive ion etching(RIE), inductively coupled plasma etching (ICP), or chemical assistedion beam etching (CAIBE), or other method. Preferably, the scribing isdiamond scribed or laser scribed or the like. In an embodiment, thesecond mirror surface comprises a reflective coating, such as silicondioxide, hafnia, titania, tantalum pentoxide, zirconia, aluminum oxide,combinations, and the like. In an embodiment, the second mirror surfacecomprises an anti-reflective coating, such alumina or aluminum oxide. Inan embodiment, the coating can be formed using electron beam deposition,thermal evaporation, RF sputtering, DC sputtering, ECR sputtering, ionbeam deposition, ion assisted deposition, reactive ion plating, anycombinations, and the like. In still other embodiments, the presentmethod may provide surface passivation to the exposed surface prior tocoating.

In an embodiment, the laser stripe has a length and width. The lengthranges from about 20 microns to about 500 microns or about 500 micronsto about 1500 microns. The stripe also has a width ranging from about0.5 microns to about 50 microns, but can be other dimensions. In anembodiment, the stripe can also be about 3 to 35 microns wide for a highpower multi-lateral-mode device or about 1 to 2 microns for a singlelateral mode laser device. In an embodiment, the width is substantiallyconstant in dimension, although there may be slight variations. Thewidth and length are often formed using a masking and etching process,which are commonly used in the art.

In an embodiment, the device is also characterized by a spontaneouslyemitted light that is polarized in substantially perpendicular to theprojection of the c-direction (in the a-direction). That is, the deviceperforms as a laser or the like. In an embodiment, the spontaneouslyemitted light is characterized by a polarization ratio of greater than0.2 to about 1 perpendicular to the c-direction. In an embodiment, thespontaneously emitted light is characterized by a wavelength rangingfrom about 400 nanometers to yield a violet emission, a blue emission, agreen emission, and/or others. In certain embodiments, the light can beemissions ranging from violet 395 nm to 420 nm; blue 430 nm to 480 nm;green 500 nm to 550 nm; or others, which may slightly vary dependingupon the application. In an embodiment, the spontaneously emitted lightis highly polarized and is characterized by a polarization ratio ofgreater than 0.4. In an embodiment, the emitted light is characterizedby a polarization ratio that is preferred.

FIG. 19 is a simplified schematic cross-sectional diagram illustrating alaser diode structure according to embodiments of the presentdisclosure. As shown, the laser device includes gallium nitridesubstrate 203, which has an underlying n-type metal back contact region201. In an embodiment, the metal back contact region is made of asuitable material such as those noted below and others.

In an embodiment, the device also has an overlying n-type galliumnitride layer 205, an active region 207, and an overlying p-type galliumnitride layer structured as a laser stripe region 211. Additionally, thedevice also includes an n-side separate confinement heterostructure(SCH) 206, p-side guiding layer or SCH 208, p-AlGaN EBL 209, among otherfeatures. In an embodiment, the device also has a p++ type galliumnitride material 213 to form a contact region. In an embodiment, the p++type contact region has a suitable thickness and may range from about 10nm to 50 nm, or other thicknesses. In an embodiment, the doping levelcan be higher than the p-type cladding region and/or bulk region. In anembodiment, the p++ type region has doping concentration ranging fromabout 10¹⁹ Mg/cm³ to 10²¹ Mg/cm³, or others. The p++ type regionpreferably causes tunneling between the semiconductor region andoverlying metal contact region. In an embodiment, each of these regionsis formed using at least an epitaxial deposition technique of metalorganic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE),or other epitaxial growth techniques suitable for GaN growth. In anembodiment, the epitaxial layer is a high quality epitaxial layeroverlying the n-type gallium nitride layer. In some embodiments, thehigh quality layer is doped, for example, with Si or O to form n-typematerial, with a dopant concentration between about 10¹⁶ cm⁻³ and 10²⁰cm⁻³.

In an embodiment, an n-type Al_(u)In_(v)Ga_(1-u-v)N layer, where 0≤u, v,u+v≤1, is deposited on the substrate. In an embodiment, the carrierconcentration may lie in the range between about 10¹⁶ cm⁻³ and 10²⁰cm⁻³. The deposition may be performed using metalorganic chemical vapordeposition (MOCVD) or molecular beam epitaxy (MBE).

As an example, the bulk GaN substrate is placed on a susceptor in anMOCVD reactor. After closing, evacuating, and back-filling the reactor(or using a load lock configuration) to atmospheric pressure, thesusceptor is heated to a temperature between about 900 to about 1200degrees Celsius in the presence of a nitrogen-containing gas. As anexample, the carrier can be hydrogen or nitrogen or others. In anembodiment, the susceptor is heated to approximately 1100 degreesCelsius under flowing ammonia. A flow of a gallium-containingmetalorganic precursor, such as trimethylgallium (TMG) ortriethylgallium (TEG) is initiated, in a carrier gas, at a total ratebetween approximately 1 and 50 standard cubic centimeters per minute(sccm). The carrier gas may comprise hydrogen, helium, nitrogen, orargon. The ratio of the flow rate of the group V precursor (e.g.,ammonia) to that of the group III precursor (trimethylgallium,triethylgallium, trimethylindium, trimethylaluminum) during growth isbetween about 2000 and about 12000. A flow of disilane in a carrier gas,with a total flow rate of between about 0.1 sccm and 10 sccm isinitiated.

In an embodiment, the laser stripe region is made of the p-type galliumnitride layer 211. In an embodiment, the laser stripe is provided by anetching process selected from dry etching or wet etching. In anembodiment, the etching process is dry, but can be others. As anexample, the dry etching process is an inductively coupled plasmaprocess using chlorine bearing species or a reactive ion etching processusing similar chemistries or combination of ICP and RIE, among othertechniques. Again as an example, the chlorine bearing species arecommonly derived from chlorine gas or the like. The device also has anoverlying dielectric region, which exposes 213 contact region, which ispreferably a p++ gallium nitride region. In an embodiment, thedielectric region is an oxide such as silicon dioxide or siliconnitride, but can be others, such as those described in more detailthroughout the present specification and more particularly below. Thecontact region is coupled to an overlying metal layer 215. The overlyingmetal layer is a multilayered structure containing gold and platinum(Ni/Au), but can be others such as gold and palladium (Pd/Au), gold,titanium, and palladium (Pd/Ti/Au) or gold and nickel (Pt/Au). In analternative embodiment, the metal layer comprises Pd/Au formed usingsuitable techniques. In an embodiment, the Ni/Au is formed viaelectron-beam deposition, sputtering, or any like techniques. Thethickness includes nickel material ranging in thickness from about 50 toabout 100 nm and gold material ranging in thickness from about 100Angstroms to about 1-3 microns, and others.

In an embodiment, the dielectric region can be made using a suitabletechnique. As an example, the technique may include reactively sputterof SiO₂ using an undoped polysilicon target (99.999% purity) with O₂ andAr. In an embodiment, the technique uses RF magnetron sputter cathodesconfigured for static deposition; sputter target; throw distance;pressure: 1-5 mT or about 2.5 mT, power: 300 to 400 W; flows: 2-3-9 sccm02, 20-50 sccm, Ar, deposition thickness: 1000-2500 A, and may includeother variations. In an embodiment, deposition may occur usingnon-absorbing, nonconductive films, e.g., Al₂O₃, Ta₂O₅, SiO₂, Ta₂O₅,ZrO₂, TiO₂, HfO₂, NbO₂. Depending upon the embodiment, the dielectricregion may be thinner, thicker, or the like. In other embodiments, thedielectric region can also include multilayer coatings, e.g., 1000 A ofSiO₂ capped with 500 A of Al₂O₃. Deposition techniques can include,among others, ebeam evaporation, thermal evaporation, RF Sputter, DCSputter, ECR Sputter, Ion Beam Deposition, Ion Assisted Deposition,reactive ion plating, combinations, and the like.

In an embodiment, the laser device has active region 207. The activeregion can include one to twenty quantum well regions according to oneor more embodiments. As an example, following deposition of the n-typeAl_(u)In_(v)Ga_(1-u-v)N layer for a predetermined period of time, so asto achieve a predetermined thickness, an active layer is deposited. Theactive layer may comprise a single quantum well or a multiple quantumwell, with 1-20 quantum wells. Preferably, the active layer may includeabout 3-9 quantum wells or more preferably 4-7 quantum wells or others.The quantum wells may comprise InGaN wells and GaN barrier layers. Inother embodiments, the well layers and barrier layers compriseAl_(w)In_(x)Ga_(1-w-x)N and Al_(y)In_(z)Ga_(1-y-z)N, respectively, where0≤w, x, y, z, w+x, y+z≤1, where w<u, y and/or x>v, z so that the bandgapof the well layer(s) is less than that of the barrier layer(s) and then-type layer. The well layers and barrier layers may each have athickness between about 1 nm and about 40 nm. In an embodiment, each ofthe thicknesses is preferably 2 nm-8 nm. In an embodiment, each wellregion may have a thickness of about 4 nm to 7 nm and each barrierregion may have a thickness of about 2 nm to about 5 nm, among others.In another embodiment, the active layer comprises a doubleheterostructure, with an InGaN or Al_(w)In_(x)Ga_(1-w-x)N layer about 10nm to 100 nm thick surrounded by GaN or Al_(y)In_(z)Ga_(1-y-z)N layers,where w<u, y and/or x>v, z. The composition and structure of the activelayer are chosen to provide light emission at a preselected wavelength.The active layer may be left undoped

In an embodiment, the active region can also include an electronblocking region, and a separate confinement heterostructure. In anembodiment, the separate confinement heterostructure (SCH) can includeAlInGaN or preferably InGaN, but can be other materials. The SCH isgenerally comprises material with an intermediate index between thecladding layers and the light emitting active layers to improveconfinement of the optical mode within the active region of the laserdevice according to an embodiment. In one or more embodiments, the SCHlayers have a preferred thickness, impurity, and configuration above andbelow the active region to confine the optical mode. Depending upon theembodiment, the upper and lower SCH can be configured differently or thesame. The electron blocking region can be on either side or both sidesof the SCH positioned above the active region according to anembodiment. In an embodiment, the SCH can range from about 10 nm toabout 150 nm, and preferably about 40 to 100 nm for the lower SCHregion. In the upper SCH region, the thickness ranges from about 20 to50 nm in an embodiment. As noted, the SCH is preferably InGaN havingabout 2% to about 5% indium or 5% to about 10% by atomic percentaccording to an embodiment.

In some embodiments, an electron blocking layer is preferably deposited.In an embodiment, the electron blocking layer comprises a gallium andnitrogen containing material including magnesium at a concentration ofabout 10¹⁶ cm⁻³ to about 10²² cm⁻³. The electron-blocking layer maycomprise Al_(s)In_(t)Ga_(1-s-t)N, where 0≤s, t, s+t≤1, with a higherbandgap than the active layer, and may be doped p-type. In one specificembodiment, the electron blocking layer comprises AlGaN with an Alcomposition ranging from 5% to 20%. In another embodiment, the electronblocking layer may not contain Al. In another embodiment, the electronblocking layer comprises an AlGaN/GaN super-lattice structure,comprising alternating layers of AlGaN and GaN, each with a thicknessbetween about 0.2 nm and about 5 nm.

As noted, the p-type gallium nitride structure, which can be a p-typedoped Al_(q)In_(r)Ga_(1-q-r)N, where 0≤q, r, q+r≤1, layer is depositedabove the active layer. The p-type layer may be doped with Mg, to alevel between about 10¹⁶ cm⁻³ and 10²² cm⁻³, and may have a thicknessbetween about 5 nm and about 1500 nm. The outermost 5 nm to 70 nm of thep-type layer may be doped more heavily than the rest of the layer, so asto enable an improved electrical contact. In an embodiment, the laserstripe is provided by an etching process selected from dry etching orwet etching. In an embodiment, the etching process is dry, but can beothers. The device also has an overlying dielectric region, whichexposes 213 contact region. In an embodiment, the dielectric region isan oxide such as silicon dioxide, but can be others.

In an embodiment, the metal contact is made of suitable material. Theelectrical contact may comprise at least one of silver, gold, aluminum,nickel, platinum, rhodium, palladium, chromium, or the like. Theelectrical contact may be deposited by thermal evaporation, electronbeam evaporation, electroplating, sputtering, or another suitabletechnique. In an embodiment, the electrical contact serves as a p-typeelectrode for the optical device. In another embodiment, the electricalcontact serves as an n-type electrode for the optical device.

FIG. 20 shows a cross-sectional schematic of a gallium and nitrogencontaining laser diode with a first, second, and third region, where thesecond region is the migration blocking region and the third regioncontains the laser stripe region.

FIG. 21 shows a cross-sectional schematic of a gallium and nitrogencontaining laser diode with a first, second, and third region, where thesecond region is the migration blocking region and the third regioncontains the laser stripe region. In this configuration there are twomigration blocking regions protecting the third region from defectsformed in the first region.

FIG. 22 shows a cross-sectional schematic of a gallium and nitrogencontaining laser diode with a first, second, and third region, where thesecond region is the migration blocking region and the third regioncontains the laser stripe region. A reflective metal layer such as Ag ora conductive oxide such as ITO is positioned above the p-type claddingregion to reduce the modal overlap with the metal layer and hence reducethe loss. In this configuration the reflective metal or conductive oxideis configured only substantially above the ridge region of the laserdiode.

FIG. 23 shows a cross-sectional schematic of a gallium and nitrogencontaining laser diode with a first, second, and third region, where thesecond region is the migration blocking region and the third regioncontains the laser stripe region. A reflective metal layer such as Ag ora conductive oxide such as ITO is positioned above the p-type claddingregion to reduce the modal overlap with the metal layer and hence reducethe loss. In this configuration the reflective metal or conductive oxideis configured both above the ridge region of the laser diode and abovethe dielectric material adjacent to the ridge region, making thedeposition process similar to what may be used to deposit the p-metal,such as a lift-off technique.

In certain embodiments, a migration blocking region may includeepitaxial layers as well as the substrate. The migration blocking layerincluding epitaxial layers such as an n-type cladding layer is formedbefore deposition of the active region in the third region.

FIG. 24 is a simulation showing loss versus wavelength for a green laserdiode epitaxial structure grown on a semipolar gallium and nitrogencontaining substrate. The different curves represent different materialsdeposited between the p-cladding region and a standard metal contactlayer such as gold, along with only air above the p-cladding. As can beseen, for a typical metal such as Titanium (Ti) the loss is about 8 cm⁻¹to 9 cm⁻¹, but can be reduced to 5 cm⁻¹ to 6 cm⁻¹ with the use of aconductive oxide like ITO and all the way down to 4 cm⁻¹ to 4.5 cm⁻¹ byusing a highly reflective metal layer such as silver (Ag). The loss isbeing reduced due to the reduced modal overlap with the metal layerabove these conductive oxide layers and reflective metal layers.According to the simulation, silver can provide a loss nearly identicalto that of having only air above the p-cladding, which is the idealcase.

In an embodiment, a ridge waveguide is fabricated using a certaindeposition, masking, and etching processes. In an embodiment, the maskcomprises photoresist (PR) or dielectric or any combination of bothand/or different types of them. The ridge mask is about 1 microns toabout 2.5 microns wide for single lateral mode applications or 2.5 μm to30 μm wide for multimode applications. The ridge waveguide is etched byion-coupled plasma (ICP), reactive ion etching (RIE), chemical assistedion beam (CAIBE) etched, or other method. The etched surface is 20 nm to250 nm above the active region. A dielectric passivation layer is thenblanket deposited by any number of commonly used methods in the art,such as sputter, e-beam, PECVD, or other methods. This passivation layercan include SiO₂, Si₃N₄, Ta₂O₅, or others. The thickness of this layeris 80 nm to 400 nm thick. An ultrasonic process is used to remove theetch mask which is covered with the dielectric. This exposes the p-GaNcontact layer. P-contact metal is deposited by e-beam, sputter, or otherdeposition technique using a PR mask to define the 2D geometry. Thecontact layer can be Ni/Au but others can be Pt/Au or Pd/Au.

In one or more preferred embodiments, the present disclosure provides alaser structure without an aluminum bearing cladding region. In anembodiment, the laser device comprises a multi-quantum well activeregion having thin barrier layers. In one or more embodiments, theactive region comprises three or more quantum well structures. Betweeneach of the quantum well structures there may be a thin barrier layer,e.g., 7 nm and less, 6 nm and less, 5 nm and less, 4 nm and less, 3 nmand less, 2 nm and less. In an embodiment, the combination of thinbarrier layers in the multi-quantum well structures enables a lowvoltage (e.g., 6 volts and less) laser diode free from use of aluminumbearing cladding regions.

In an embodiment, the present disclosure provides an optical device. Theoptical device has a gallium and nitrogen containing substrate includinga (60-6-1), (60-61), (50-5-1), (50-51), (40-4-1), (40-41), (30-3-1), a(30-31), a (20-2-1), a (20-21), a (30-3-2), a (30-32), and/or an offcutorientation. or offcuts thereof crystalline surface region orientation,which may be off-cut. The device preferably has an n-type claddingmaterial overlying the n-type gallium and nitrogen containing materialaccording to an embodiment. The n-type cladding material may be formedfrom GaN, AlGaN, InAlGaN, or a combination and ranges in thickness fromabout 1 μm to about 5 μm according to an embodiment. The n-type claddingmaterial may be doped with silicon or oxygen. The device also has anactive region comprising at least three quantum wells. Each of thequantum wells has a thickness of 3.0 nm and greater or 5.5 nm andgreater, and one or more barrier layers. Each of the barrier layers hasa thickness ranging from about 2 nm to about 4 nm or about 4 nm to about8 nm or about 8 nm to about 20 nm and is configured between a pair ofquantum wells according to an embodiment. At least one or each of thebarrier layers has a thickness ranging from about 2 nm to about 4 nm andis configured between a pair of quantum wells or adjacent to a quantumwell according to an embodiment. At least one or each of the barrierlayers has a thickness ranging from about 3.5 nm to about 6.5 nm and isconfigured between a pair of quantum wells or adjacent to a quantum wellaccording to an embodiment. Preferably, the device has a p-type claddingmaterial overlying the active region. Preferably, the p-type claddingmaterial may be formed from GaN, AlGaN, InAlGaN, or a combination andranges in thickness from about 0.4 μm to about 1 μm according to anembodiment. The p-type cladding material may be doped with magnesium. Inan embodiment, the active region is configured for a forward voltage ofless than about 6V or less than about 5V for the device for an outputpower of 60 mW or 100 mW and greater.

In yet an alternative embodiment, the present disclosure provides anoptical device. The device has a gallium and nitrogen containingsubstrate including a (60-6-1), (60-61), (50-5-1), (50-51), (40-4-1),(40-41), (30-3-1), a (30-31), a (20-2-1), a (20-21), a (30-3-2), a(30-32), and/or an offcut orientation. The device also has an n-typecladding material overlying the n-type gallium and nitrogen containingmaterial. The n-type cladding material may be formed from GaN, AlGaN,InAlGaN, or a combination of any of the foregoing, and may range inthickness from about 1 μm to about 5 μm according to an embodiment. Then-type cladding material may be doped with silicon or oxygen. The devicefurther has an active region comprising at least three quantum wells.Each of the quantum wells has a thickness of 2.0 nm and greater or 3.5nm and greater or 5 nm and greater and one or more barrier layersaccording to an embodiment. Each of the barrier layers has a thicknessranging from about 2 nm to about 4 nm or about 4 nm to about 8 nm orabout 8 nm to about 20 nm according to an embodiment. Each of thebarrier layers is configured between a pair of quantum wells accordingto one or more embodiments. At least one or each of the barrier layershas a thickness ranging from about 2 nm to about 5 nm and is configuredbetween a pair of quantum wells or adjacent to a quantum well accordingto an embodiment. At least one or each of the barrier layers has athickness ranging from about 4 nm to about 8 nm and is configuredbetween a pair of quantum wells or adjacent to a quantum well accordingto an embodiment. The device also has a p-type cladding materialoverlying the active region. Preferably, the p-type cladding materialmay be formed from GaN, AlGaN, InAlGaN, or a combination and ranges inthickness from about 0.4 μm to about 1 μm according to an embodiment.The p-type cladding material may be doped with magnesium. The deviceoptionally has a p-type material overlying the p-type cladding material.

In other embodiments, the invention provides yet an alternative opticaldevice, which has a gallium and nitrogen containing substrate includinga (60-6-1), (60-61), (50-5-1), (50-51), (40-4-1), (40-41), (30-3-1), a(30-31), a (20-2-1), a (20-21), a (30-3-2), a (30-32), or offcutsthereof crystalline surface region orientation. An n-type claddingmaterial is overlying the n-type gallium and nitrogen containingmaterial. Preferably, the n-type cladding material is substantially freefrom an aluminum bearing material. The device has an active regioncomprising at least three quantum wells, each of which has a thicknessof 2.5 nm or 3.5 nm and greater. The device has one or more barrierlayers, each of which has a thickness ranging from about 2 nm to about 4nm or about 4 nm to about 8 nm or about 8 nm to about 20 nm in one ormore alternative embodiments. Preferably, each of the barrier layers isconfigured between a pair of quantum wells according to an embodiment.The device also has a p-type cladding material overlying the activeregion according to an embodiment. The p-type cladding material issubstantially free from an aluminum bearing material according to anembodiment. The device also has a p-type material overlying the p-typecladding material.

In other embodiments, the invention provides a method of fabricating anoptical device, which has a gallium and nitrogen containing substrateincluding a (60-6-1), (60-61), (50-5-1), (50-51), (40-4-1), (40-41),(30-3-1), a (30-31), a (20-2-1), a (20-21), a (30-3-2), a (30-32), oroffcuts thereof crystalline surface region orientation. An n-typecladding material is overlying the n-type gallium and nitrogencontaining material. Preferably, the n-type cladding material issubstantially free from an aluminum bearing material. The methodincludes forming an active region comprising at least three quantumwells, each of which has a thickness of 2.5 nm or 3.5 nm and greater.The device has one or more barrier layers, each of which has an n-typeimpurity characteristic and a thickness ranging from about 2 nm to about4 nm or about 4 nm to about 8 nm or about 8 nm to about 20 nm in one ormore alternative embodiments. Preferably, each of the barrier layers isconfigured between a pair of quantum wells according to an embodiment.The method also includes forming a p-type cladding material overlyingthe active region according to an embodiment. The p-type claddingmaterial is substantially free from an aluminum bearing materialaccording to an embodiment. The method also includes forming a p-typematerial overlying the p-type cladding material.

In an embodiment, the present disclosure provides an optical device,such as a laser diode. The device has a gallium and nitrogen containingsubstrate including a (60-6-1), (60-61), (50-5-1), (50-51), (40-4-1),(40-41), (30-3-1), a (30-31), a (20-2-1), a (20-21), a (30-3-2), a(30-32), or offcuts thereof crystalline surface region orientation,which may be off-cut according to one or more embodiments. The devicehas an n-type cladding material overlying the n-type gallium andnitrogen containing material. The n-type cladding material may be formedfrom GaN, AlGaN, InAlGaN, or a combination of any of the forgoing andmay range in thickness from about 1 μm to about 5 μm according to anembodiment. The n-type cladding material may be doped with silicon oroxygen. The device also has an active region comprising at least threequantum wells. In an embodiment, each of the quantum wells has athickness of 2.0 nm or 3.5 nm and greater and one or more barrier layersaccording to an embodiment. Each of the barrier layers has a n-typecharacteristic and a thickness ranging from about 2 nm to about 4.5 nmin an embodiment. Each of the barrier layers has a p-type characteristicand a thickness ranging from about 3.5 nm to about 7 nm in analternative specific embodiment. In an embodiment, each of the barrierlayers is configured between a pair of quantum wells. The device alsohas a p-type cladding material overlying the active region. Preferably,the p-type cladding material may be formed from GaN, AlGaN, InAlGaN, ora combination of any of the foregoing and may range in thickness fromabout 0.3 μm to about 1 μm according to an embodiment. The p-typecladding material may be doped with magnesium. And overlying p-typematerial is included. In an embodiment, the active region is configuredfor a forward voltage of less than about 6 V or less than about 7V forthe device for an output power of 60 mW and greater. In otherembodiments for nonpolar m-plane devices or semipolar (60-6-1), (60-61),(50-5-1), (50-51), (40-4-1), (40-41), (30-3-1), a (30-31), a (20-2-1), a(20-21), a (30-3-2), a (30-32), or offcuts thereof planes, operable inthe blue (430 nm-475 nm) and green (505-530 nm), the present method andstructure include five (5) or more thick quantum wells of greater than 4nm or 5 nm in thickness and thin barriers that are 2-4 nm in thickness.

In one or more embodiments, the present disclosure includes a laserdiode substantially free from an aluminum containing cladding region. Toform the laser diode without an aluminum containing cladding region, thepresent laser diode includes three or more quantum wells to provideenough confinement of the optical mode for sufficient gain to reachlasing. However, when the number of quantum wells increases in theactive region, the forward voltage of the diode can increase, as atradeoff. We have determined that the forward voltage of the diode canbe reduced in multi-quantum well active regions by way of the use ofthin barriers on the order of 3 nm to 4 nm, which are much thinner thanconventional lasers such as those in Yoshizumi et al., “Continuous-Waveoperation of 520 nm Green InGaN-Based Laser Diodes on Semi-Polar {20-21}GaN Substrates,” Applied Physics Express, 2 (2009) 092101. We have alsodetermined that the forward voltage can be reduced in multi-quantum wellactive regions by adding p or n-type dopant species to the active regionaccording to one or more other embodiments. Although any one orcombination of these approached can be used, we believe it may bepreferable to use the thin barrier approach to avoid adding impuritiesto the active region. The impurities may change optical losses and alterthe electrical junction placement according to one or more embodiments.Accordingly, the present disclosure provides a laser device and methodwith low voltage on (60-6-1), (60-61), (50-5-1), (50-51), (40-4-1),(40-41), (30-3-1), a (30-31), a (20-2-1), a (20-21), a (30-3-2), a(30-32), or offcuts thereof.

The device has a gallium and nitrogen containing substrate member havinga (60-6-1), (60-61), (50-5-1), (50-51), (40-4-1), (40-41), (30-3-1), a(30-31), a (20-2-1), a (20-21), a (30-3-2), a (30-32), or offcutsthereof crystalline surface region. The device has an n-type gallium andnitrogen containing cladding material. In an embodiment, the n-typegallium and nitrogen containing cladding material is substantially freefrom an aluminum species, which leads to imperfections, defects, andother limitations. The device also has an active region includingmultiple quantum well structures overlying the n-type gallium andnitrogen containing cladding material. In one or more preferredembodiments, the device also has thin barrier layers configured with themultiple well structures. The device has a p-type gallium and nitrogencontaining cladding material overlying the active region. In anembodiment, the p-type gallium and nitrogen containing cladding materialis substantially free from an aluminum species. The device preferablyincludes a laser stripe region configured from at least the activeregion and characterized by a cavity orientation substantially parallelto a projection of the c-direction. The laser stripe region has a firstend and a second end. The device also has a first cleaved or etchedfacet provided on the first end of the laser stripe region and a secondcleaved or etched facet provided on the second end of the laser striperegion. Depending upon the embodiment, the facets may be cleaved,etched, or a combination of cleaved and etched. In yet otherembodiments, the present device includes a gallium and nitrogencontaining electron-blocking region that is substantially free fromaluminum species. In yet other embodiments, the device does not includeany electron-blocking layer or yet in other embodiments, there is noaluminum in the cladding layers and/or electron blocking layer, althoughother embodiments include aluminum containing blocking layers. In stillother embodiments, the optical device and method are free from anyaluminum material, which leads to defects, imperfections, and the like.

In some preferred embodiments, the present method and structure issubstantially free from InAlGaN or aluminum bearing species in thecladding layers as conventional techniques, such as those in Yoshizumiet al., “Continuous-Wave operation of 520 nm Green InGaN-Based LaserDiodes on Semi-Polar {20-21} GaN Substrates,” Applied Physics Express 2(2009) 092101. That is, the present laser structure and method aresubstantially free from any aluminum species in the cladding region.Aluminum is generally detrimental. Aluminum often leads to introductionof oxygen in the reactor, which can act as non radiative recombinationcenters to reduce the radiative efficiency and introduce otherlimitations. We also determined that oxygen can compensate p-typedopants in the p-cladding to cause additional resistivity in the opticaldevice. In other aspects, we also determined that aluminum isdetrimental to the MOCVD reactor and can react or pre-react with othergrowth precursors. Use of aluminum containing cladding layers is alsocumbersome and can take additional time to grow. In fact, by usingsubstantially Al-free cladding layers MOCVD growth throughput can beincreased by 2-4× drastically reducing the cost associated with growth.Accordingly, it is believed that the aluminum cladding free laser methodand structure are generally more efficient to grow than conventionallaser structures.

Moreover, the present invention provides an optical device that issubstantially free from aluminum bearing cladding materials. The devicehas a gallium and nitrogen containing substrate member having a (30-3-1)or offcut crystalline surface region. The device has an n-type galliumand nitrogen containing cladding material. In a specific embodiment, then-type gallium and nitrogen containing cladding material issubstantially free from an aluminum species, which leads toimperfections, defects, and other limitations. The device also has anactive region including multiple quantum well structures overlying then-type gallium and nitrogen containing cladding material. In one or morepreferred embodiments, the device also has thin barrier layersconfigured with the multiple well structures. The device has a p-typegallium and nitrogen containing cladding material overlying the activeregion. In a preferred embodiment, the p-type gallium and nitrogencontaining cladding material is substantially free from an aluminumspecies. The device preferably includes a laser stripe region configuredfrom at least the active region and characterized by a cavityorientation substantially parallel to a projection in a c-direction. Thelaser strip region has a first end and a second end. The device also hasa first etched or etched facet provided on the first end of the laserstripe region and a second etched or etched facet provided on the secondend of the laser stripe region. Depending upon the embodiment, thefacets may be etched, etched, or a combination of cleaved and etched. Inyet other embodiments, the present device includes a gallium andnitrogen containing electron blocking region that is substantially freefrom aluminum species. In yet other embodiments, the device does notinclude any electron blocking layer or yet in other embodiments, thereis no aluminum in the cladding layers and/or electron blocking layer,although other embodiments include aluminum containing blocking layers.In still other embodiments, the optical device and method are free fromany aluminum material, which leads to defects, imperfections, and thelike. Further details of these limitations can be found throughout thepresent specification and more particularly below.

In preferred embodiments, the present method and structure issubstantially free from InAlGaN or aluminum bearing species in thecladding layers as conventional techniques, such as those in Yoshizumiet al., “Continuous-Wave operation of 520 nm Green InGaN-Based LaserDiodes on Semi-Polar {20-21} GaN Substrates,” Applied Physics Express 2(2009) 092101. That is, the present laser structure and method aresubstantially free from any aluminum species in the cladding region.Aluminum is generally detrimental. Aluminum often leads to introductionof oxygen in the reactor, which can act as non radiative recombinationcenters to reduce the radiative efficiency and introduce otherlimitations. We also determined that oxygen can compensate p-typedopants in the p-cladding to cause additional resistivity in the opticaldevice. In other aspects, we also determined that aluminum isdetrimental to the MOCVD reactor and can react or pre-react with othergrowth precursors. Use of aluminum cladding layers is also cumbersomeand can take additional time to grow. Accordingly, it is believed thatthe aluminum cladding free laser method and structure are generally moreefficient to grow than conventional laser structures. Further benefitsare described throughout the present specification and more particularlybelow.

In alternative example, the present invention provides a green laserdiode configured using a semipolar gallium and nitrogen containing bulksubstrate member, as described in more detail below, which has etchedfacets.

In preferred embodiments, the invention provides a laser structurewithout an aluminum bearing cladding region. In a specific embodiment,the laser device comprises a multi-quantum well active region havingthin barrier layers, with the active region comprising three or morequantum well structures. Between each of the quantum well structures isa thin barrier layer, e.g., 8 nm and less, 7 nm and less, 6 nm and less,5 nm and less, 4 nm and less, 3 nm and less, 2 nm and less, 1.5 nm andless. In a preferred embodiment, the combination of thin barrier layersconfigured in the multi-quantum well structures enables a low voltage(e.g., 7 volts and less, 6 volts and less) laser diode free from use ofaluminum bearing cladding regions.

In one embodiment, the optical device has a gallium and nitrogencontaining substrate including a {20-21} crystalline surface regionorientation, which may be off-cut. The device preferably has an n-typecladding material overlying the n-type gallium and nitrogen containingmaterial according to a specific embodiment. The n-type claddingmaterial is substantially free from an aluminum bearing material. Thedevice also has an active region comprising at least three quantumwells. Each of the quantum wells has a thickness of 2.5 nm and greateror 3.5 nm and greater and one or more barrier layers. Each of thebarrier layers has a thickness ranging from about 2 nm to about 4 nm orabout 3 nm to about 6.5 nm and is configured between a pair of quantumwells according to a specific embodiment. At least one or each of thebarrier layers has a thickness ranging from about 2 nm to about 4 nm andis configured between a pair of quantum wells or adjacent to a quantumwell according to a specific embodiment. At least one or each of thebarrier layers has a thickness ranging from about 3 nm to about 6.5 nmand is configured between a pair of quantum wells or adjacent to aquantum well according to a specific embodiment. Preferably, the devicehas a p-type cladding material overlying the active region. Preferably,the p-type cladding material is substantially free from an aluminumbearing material according to a specific embodiment. In a preferredembodiment, the active region is configured operably for a forwardvoltage of less than about 7V or less than about 6V for the device foran output power of 60 mW and greater.

In yet an alternative embodiment, the present invention provides anoptical device. The device has a gallium and nitrogen containingsubstrate including a {20-21} crystalline surface region orientation.The device also has an n-type cladding material overlying the n-typegallium and nitrogen containing material. The n-type cladding materialis substantially free from an aluminum bearing material. The devicefurther has an active region comprising at least two quantum wells. Eachof the quantum wells has a thickness of 2.5 nm and greater or 3.5 nm andgreater and one or more barrier layers according to a specificembodiment. Each of the barrier layers has a thickness ranging fromabout 2 nm to about 5 nm or about 3 nm to about 8 nm according to aspecific embodiment. Each of the barrier layers is configured between apair of quantum wells according to one or more embodiments. At least oneor each of the barrier layers has a thickness ranging from about 2 nm toabout 5 nm and is configured between a pair of quantum wells or adjacentto a quantum well according to a specific embodiment. At least one oreach of the barrier layers has a thickness ranging from about 3 nm toabout 8 nm and is configured between a pair of quantum wells or adjacentto a quantum well according to a specific embodiment. The device alsohas a p-type cladding material overlying the active region. The p-typecladding material is substantially free from an aluminum bearingmaterial according to a preferred embodiment. The device optionally hasa p-type material overlying the p-type cladding material.

In other embodiments, the invention provides yet an alternative opticaldevice, which has a gallium and nitrogen containing substrate includinga {20-21} crystalline surface region orientation. An n-type claddingmaterial is overlying the n-type gallium and nitrogen containingmaterial. Preferably, the n-type cladding material is substantially freefrom an aluminum bearing material. The device has an active regioncomprising at least two quantum wells, each of which has a thickness of2.5 nm and greater. The device has one or more barrier layers, each ofwhich has an n-type impurity characteristic and a thickness ranging fromabout 2 nm to about 5 nm or about 3 nm to about 8 nm in one or morealternative embodiments. Preferably, each of the barrier layers isconfigured between a pair of quantum wells according to a specificembodiment. The device also has a p-type cladding material overlying theactive region according to a specific embodiment. The p-type claddingmaterial is substantially free from an aluminum bearing materialaccording to a specific embodiment. The device also has a p-typematerial overlying the p-type cladding material.

In other embodiments, the invention provides a method of fabricating anoptical device, which has a gallium and nitrogen containing substrateincluding a {20-21} crystalline surface region orientation. An n-typecladding material is overlying the n-type gallium and nitrogencontaining material. Preferably, the n-type cladding material issubstantially free from an aluminum bearing material. The methodincludes forming an active region comprising at least two quantum wells,each of which has a thickness of 2.5 nm and greater. The device has oneor more barrier layers, each of which has an n-type impuritycharacteristic and a thickness ranging from about 2 nm to about 5 nm orabout 3 nm to about 8 nm in one or more alternative embodiments.Preferably, each of the barrier layers is configured between a pair ofquantum wells according to a specific embodiment. The method alsoincludes forming a p-type cladding material overlying the active regionaccording to a specific embodiment. The p-type cladding material issubstantially free from an aluminum bearing material according to aspecific embodiment. The method also includes forming a p-type materialoverlying the p-type cladding material.

In a specific embodiment, the present invention provides an opticaldevice, such as a laser diode. The device has a gallium and nitrogencontaining substrate including a {20-21} crystalline surface regionorientation, which may be off-cut according to one or more embodiments.The device has an n-type cladding material overlying the n-type galliumand nitrogen containing material. In a preferred embodiment, the n-typecladding material is substantially free from an aluminum bearingmaterial. The device also has an active region comprising at least twoquantum wells. In a specific embodiment, each of the quantum wells has athickness of 2.5 nm and greater and one or more barrier layers accordingto a specific embodiment. Each of the barrier layers has a p-typecharacteristic and a thickness ranging from about 2 nm to about 3.5 nmin a specific embodiment. Each of the barrier layers has a p-typecharacteristic and a thickness ranging from about 3.5 nm to about 7 nmin an alternative specific embodiment. In a preferred embodiment, eachof the barrier layers is configured between a pair of quantum wells. Thedevice also has a p-type cladding material overlying the active region.Preferably, the p-type cladding material is substantially free from analuminum bearing material. And overlying p-type material is included. Ina preferred embodiment, the active region is configured for a forwardvoltage of less than about 6V or less than about 7V for the device foran output power of 60 mW and greater.

In one or more embodiments, the present invention includes a laser diodesubstantially free from an aluminum containing cladding region. To formthe laser diode without an aluminum containing cladding region, thepresent laser diode includes three or more quantum wells to provideenough confinement of the optical mode for sufficient gain to reachlasing. However, when the number of quantum wells increases in theactive region, the forward voltage of the diode can increase, as atradeoff. We have determined that the forward voltage of the diode canbe reduced in multi-quantum well active regions by way of the use ofthin barriers on the order of 5 nm, which are much thinner thanconventional lasers such as those in Yoshizumi et al., “Continuous-Waveoperation of 520 nm Green InGaN-Based Laser Diodes on Semi-Polar {20-21}GaN Substrates,” Applied Physics Express 2 (2009) 092101. We have alsodetermined that the forward voltage can be reduced in multi-quantum wellactive regions by adding p or n-type dopant species to the active regionaccording to one or more other embodiments. Although any one orcombination of these approached can be used, we believe it may bepreferable to use the thin barrier approach to avoid adding impuritiesto the active region. The impurities may change optical losses and alterthe electrical junction placement according to one or more embodiments.Accordingly, the present invention provides a laser device and methodthat is free from aluminum-containing cladding regions with low voltageon {20-21} substrates.

Moreover, the present invention provides an optical device that issubstantially free from aluminum bearing cladding materials. The devicehas a gallium and nitrogen containing substrate member having a {20-21}crystalline surface region. The device has an n-type gallium andnitrogen containing cladding material. In a specific embodiment, then-type gallium and nitrogen containing cladding material issubstantially free from an aluminum species, which leads toimperfections, defects, and other limitations. The device also has anactive region including multiple quantum well structures overlying then-type gallium and nitrogen containing cladding material. In one or morepreferred embodiments, the device also has thin barrier layersconfigured with the multiple well structures. The device has a p-typegallium and nitrogen containing cladding material overlying the activeregion. In a preferred embodiment, the p-type gallium and nitrogencontaining cladding material is substantially free from an aluminumspecies. The device preferably includes a laser stripe region configuredfrom at least the active region and characterized by a cavityorientation substantially parallel to a projection in a c-direction. Thelaser strip region has a first end and a second end. The device also hasa first etched facet provided on the first end of the laser striperegion and a second etched facet provided on the second end of the laserstripe region. In yet other embodiments, the present device includes agallium and nitrogen containing electron blocking region that issubstantially free from aluminum species. In yet other embodiments, thedevice does not include any electron blocking layer or yet in otherembodiments, there is no aluminum in the cladding layers and/or electronblocking layer, although other embodiments include aluminum containingblocking layers. In still other embodiments, the optical device andmethod are free from any aluminum material, which leads to defects,imperfections, and the like.

In preferred embodiments, the present method and structure issubstantially free from InAlGaN or aluminum bearing species in thecladding layers as conventional techniques, such as those in Yoshizumiet al., “Continuous-Wave operation of 520 nm Green InGaN-Based LaserDiodes on Semi-Polar {20-21} GaN Substrates,” Applied Physics Express 2(2009) 092101. That is, the present laser structure and method aresubstantially free from any aluminum species in the cladding region.Aluminum is generally detrimental. Aluminum often leads to introductionof oxygen in the reactor, which can act as non radiative recombinationcenters to reduce the radiative efficiency and introduce otherlimitations. We also determined that oxygen can compensate p-typedopants in the p-cladding to cause additional resistivity in the opticaldevice. In other aspects, we also determined that aluminum isdetrimental to the MOCVD reactor and can react or pre-react with othergrowth precursors. Use of aluminum cladding layers is also cumbersomeand can take additional time to grow. Accordingly, it is believed thatthe aluminum cladding free laser method and structure are generally moreefficient to grow than conventional laser structures.

In a specific embodiment on the {20-21} GaN, the device has a laserstripe region formed overlying a portion of the off-cut crystallineorientation surface region. In a specific embodiment, the laser striperegion is characterized by a cavity orientation substantially in aprojection of a c-direction, which is substantially normal to ana-direction. In a specific embodiment, the laser strip region has afirst end and a second end, each of which is etched. In a preferredembodiment, the device is formed on a projection of a c-direction on a{20-21} gallium and nitrogen containing substrate having a pair ofetched mirror structures, which face each other.

In a preferred embodiment, the device has a first etched facet providedon the first end of the laser stripe region and a second etched facetprovided on the second end of the laser stripe region. In one or moreembodiments, the first etched is substantially parallel with the secondetched facet. Mirror surfaces are formed on each of the etched surfaces.The first etched facet comprises a first mirror surface. In a specificembodiment, the first mirror surface comprises a reflective coating. Thereflective coating is selected from silicon dioxide, hafnia, andtitania, tantalum pentoxide, zirconia, including combinations, and thelike. Depending upon the embodiment, the first mirror surface can alsocomprise an anti-reflective coating.

Also in a preferred embodiment, the second etched facet comprises asecond mirror surface. In a specific embodiment, the second mirrorsurface comprises a reflective coating, such as silicon dioxide, hafnia,and titania, tantalum pentoxide, zirconia, combinations, and the like.In a specific embodiment, the second mirror surface comprises ananti-reflective coating.

In a specific embodiment, the laser stripe has a length and width. Thelength ranges from about 50 microns to about 3000 microns or preferablyfrom about 50 microns to 300 microns, 300 microns to about 90 microns orabout 90 microns to about 1600 um microns. The strip also has a widthranging from about 0.5 microns to about 50 microns or preferably between1 microns to about 1.5 microns, about 1.5 microns to about 2.0 microns,about 2.0 microns to about 4 microns, or about 4 microns to about 35microns but can be other dimensions. In a specific embodiment, the widthis substantially constant in dimension, although there may be slightvariations. The width and length are often formed using a masking andetching process, which are commonly used in the art.

In a specific embodiment, the present invention provides an alternativedevice structure capable of emitting 501 nm and greater light in a ridgelaser embodiment having etched facets. The device is provided, forexample, with one or more of the following epitaxially grown elements:

an n-GaN cladding layer with a thickness from 100 nm to 3000 nm with Sidoping level of 5E17 cm⁻³ to 3E18 cm⁻³;

an n-side SCH layer comprising InGaN with molar fraction of InN ofbetween 3% and 15% and thickness from 20 nm to 150 nm;

multiple quantum well active region layers comprising at least two 2.0nm to 7.5 nm InGaN quantum wells separated by thin 1.5 nm and greater,and optionally up to about 8 nm, GaN barriers

a barrier region formed overlying the active region;

a p-side SCH layer comprising InGaN with molar a fraction of InN ofbetween 0% and 15% and a thickness from 15 nm to 100 nm;

an electron blocking layer comprising AlGaN with molar fraction ofaluminum of between 5% and 20% and thickness from 5 nm to 20 nm anddoped with Mg;

a p-GaN cladding layer with a thickness from 400 nm to 1500 nm with Mgdoping level of 2E17 cm⁻³ to 2E19 cm⁻³; and

a p++-GaN contact layer with a thickness from 15 nm to 50 nm with Mgdoping level of 1E19 cm⁻³ to 1E21 cm⁻³.

Of course there can be other embodiments such as the use of p-side GaNguiding layer in place of the p-SCH, the use of multiple differentlayers in the SCH regions, or the omission of the EBL layer. Again,there can be other variations, modifications, and alternatives.

In an example, a laser device is fabricated on a {20-21} substrateaccording to an embodiment of the present invention. The laser deviceincludes gallium nitride substrate, which has an underlying n-type metalback contact region. In a specific embodiment, the metal back contactregion is made of a suitable material such as those noted below andothers. Further details of the contact region can be found throughoutthe present specification, and more particularly below.

In a specific embodiment, the device also has an overlying n-typegallium nitride layer, an active region, and an overlying p-type galliumnitride layer structured as a laser stripe region. In a specificembodiment, each of these regions is formed using at least an epitaxialdeposition technique of metal organic chemical vapor deposition (MOCVD),molecular beam epitaxy (MBE), or other epitaxial growth techniquessuitable for GaN growth. In a specific embodiment, the epitaxial layeris a high quality epitaxial layer overlying the n-type gallium nitridelayer. In some embodiments the high quality layer is doped, for example,with Si or O to form n-type material, with a dopant concentrationbetween about 10¹⁶ cm⁻³ and 10²⁰ cm⁻³.

In a specific embodiment, an n-type Al_(u)In_(v)Ga_(1-u-v)N layer, where0≤u, v, u+v≤1, is deposited on the substrate. In a specific embodiment,the carrier concentration may lie in the range between about 10¹⁶ cm⁻³and 10²⁰ cm⁻³. The deposition may be performed using metalorganicchemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

As an example, the bulk GaN substrate is placed on a susceptor in anMOCVD reactor. After closing, evacuating, and back-filling the reactor(or using a load lock configuration) to atmospheric pressure, thesusceptor is heated to a temperature between about 1000 and about 1200degrees Celsius in the presence of a nitrogen-containing gas. In onespecific embodiment, the susceptor is heated to approximately 900 to1100 degrees Celsius under flowing ammonia. A flow of agallium-containing metalorganic precursor, such as trimethylgallium(TMG) or triethylgallium (TEG) is initiated, in a carrier gas, at atotal rate between approximately 1 and 50 standard cubic centimeters perminute (sccm). The carrier gas may comprise hydrogen, helium, nitrogen,or argon. The ratio of the flow rate of the group V precursor (ammonia)to that of the group III precursor (trimethylgallium, triethylgallium,trimethylindium, trimethylaluminum) during growth is between about 2000and about 12000. A flow of disilane in a carrier gas, with a total flowrate of between about 0.1 sccm and 10 sccm, is initiated.

In a specific embodiment, the laser stripe region is made of the p-typegallium nitride layer. In a specific embodiment, the laser stripe isprovided by an etching process selected from dry etching or wet etching.In a preferred embodiment, the etching process is dry, but can beothers. As an example, the dry etching process is an inductively coupledprocess using chlorine bearing species or a reactive ion etching processusing similar chemistries. Again as an example, the chlorine bearingspecies are commonly derived from chlorine gas or the like. The devicealso has an overlying dielectric region, which exposes contact region.In a specific embodiment, the dielectric region is an oxide such assilicon dioxide or silicon nitride, but can be others. The contactregion is coupled to an overlying metal layer. The overlying metal layeris a multilayered structure containing gold and platinum (Pt/Au), nickelgold (Ni/Au), palladium and gold (Pd/Ti), but can be others.

In a specific embodiment, the laser device has active region. The activeregion can include one to twenty quantum well regions according to oneor more embodiments. As an example following deposition of the n-typeAl_(u)In_(v)Ga_(1-u-v)N layer for a predetermined period of time, so asto achieve a predetermined thickness, an active layer is deposited. Theactive layer may comprise multiple quantum wells, with 2-10 quantumwells. The quantum wells may comprise InGaN with GaN barrier layersseparating them. In other embodiments, the well layers and barrierlayers comprise Al_(w)In_(x)Ga_(1-w-x)N and Al_(y)In_(z)Ga_(1-y-z)N,respectively, where 0≤w, x, y, z, w+x, y+z≤1, where w<u, y and/or x>v, zso that the bandgap of the well layer(s) is less than that of thebarrier layer(s) and the n-type layer. The well layers and barrierlayers may each have a thickness between about 1 nm and about 20 nm. Thecomposition and structure of the active layer are chosen to providelight emission at a preselected wavelength. The active layer may be leftundoped (or unintentionally doped) or may be doped n-type or p-type.

In a specific embodiment, the active region can also include an electronblocking region, and a separate confinement heterostructure. In someembodiments, an electron blocking layer is preferably deposited. Theelectron-blocking layer may comprise Al_(s)In_(t)Ga_(1-s-t)N, where 0≤s,t, s+t≤1, with a higher bandgap than the active layer, and may be dopedp-type. In one specific embodiment, the electron blocking layercomprises AlGaN. In another embodiment, the electron blocking layercomprises an AlGaN/GaN super-lattice structure, comprising alternatinglayers of AlGaN and GaN, each with a thickness between about 0.2 nm andabout 5 nm.

In a specific embodiment, the action region structure does not includean AlGaN EBL layer. That is, the laser device is free from any electronblocking layer, which is optional in such embodiment.

As noted, the p-type gallium nitride structure is deposited above theelectron blocking layer and active layer(s). The p-type layer may bedoped with Mg, to a level between about 10¹⁶ cm⁻³ and 10²² cm⁻³, and mayhave a thickness between about 5 nm and about 1000 nm. The outermost 1nm to 50 nm of the p-type layer may be doped more heavily than the restof the layer, so as to enable an improved electrical contact. In aspecific embodiment, the laser stripe is provided by an etching processselected from dry etching or wet etching. In a preferred embodiment, theetching process is dry, but can be others. The device also has anoverlying dielectric region, which exposes a contact region. In aspecific embodiment, the dielectric region is an oxide such as silicondioxide.

In a specific embodiment, the metal contact is made of suitablematerial. The electrical contact may comprise at least one of silver,gold, aluminum, nickel, platinum, rhodium, palladium, chromium, or thelike. The electrical contact may be deposited by thermal evaporation,electron beam evaporation, electroplating, sputtering, or anothersuitable technique. In a preferred embodiment, the electrical contactserves as a p-type electrode for the optical device. In anotherembodiment, the electrical contact serves as an n-type electrode for theoptical device.

In an example, a laser device includes a starting material such as abulk nonpolar or semipolar GaN substrate, but can be others. In aspecific embodiment, the device is configured to achieve emissionwavelength ranges of 390 nm to 420 nm, 420 nm to 440 nm, 440 nm to 470nm, 470 nm to 490 nm, 490 nm to 510 nm, and 510 nm to 540 nm, but can beothers.

In a preferred embodiment, the growth structure is configured usingbetween 3 and 5 or 5 and 7 or 7 and 9 quantum wells positioned betweenn-type GaN and p-type GaN cladding layers. In a specific embodiment, then-type GaN cladding layer ranges in thickness from 500 nm to 4000 nm andhas an n-type dopant such as Si with a doping level of between 5E17 cm⁻³and 5E18 cm⁻³. In a specific embodiment, the p-type GaN cladding layerranges in thickness from 500 nm to 1200 nm and has a p-type dopant suchas Mg with a doping level of between 1E17 cm⁻³ and 7E19 cm⁻³. In aspecific embodiment, the Mg doping level is graded such that theconcentration may be lower in the region closer to the quantum wells.

In a specific preferred embodiment, the quantum wells have a thicknessof between 2.5 nm and 4 nm, 4 nm and 5.5 nm or 5.5 nm and 8 nm, but canbe others. In a specific embodiment, the quantum wells may be separatedby barrier layers with thicknesses between 2 nm and 3.5 nm or 3.5 nm and6 nm or 6 nm and 8 nm. The quantum wells and the barriers togethercomprise a multiple quantum well (MQW) region.

In a preferred embodiment, the device has barrier layers formed fromGaN, InGaN, AlGaN, or InAlGaN. In a specific embodiment using InGaNbarriers, the indium contents range from 0% to 5% (mole percent), butcan be others. Also, it should be noted that % of indium or aluminum isin a molar fraction, not weight percent.

An InGaN separate confinement heterostructure layer (SCH) can bepositioned between the n-type GaN cladding and the MQW region accordingto one or more embodiments. Typically, such separate confinement layeris also referred to as the n-side SCH. The n-side SCH layer ranges inthickness from 10 nm to 60 nm or 60 nm to 150 nm and ranges in indiumcomposition from 1% to 12% (mole percent of InN), but can be others. Ina specific embodiment, the n-side SCH layer may be doped with an n-typedopant such as Si.

In yet another preferred embodiment, an InGaN separate confinementheterostructure layer (SCH) is positioned between the p-type GaNcladding and the MQW region, which is called the p-side SCH. In aspecific embodiment, the p-side SCH layer ranges in thickness from 10 nmto 40 nm or 40 nm to 150 nm and ranges in indium composition from 0% to10% (mole percent), but can be others. The p-side SCH layer may be dopedwith a p-type dopant such as Mg.

In another embodiment, the structure may contain both an n-side SCH anda p-side SCH. In another embodiment, the p-side SCH can be replaced withp-side GaN guiding layer. In another embodiment, the n-side and/orp-side SCH regions may contain multiple layers.

In another embodiment, the structure may contain a GaN guiding layer onthe p-side positioned between the p-type GaN cladding layer and the MQWregion. This GaN guiding layer may range in thickness from 10 nm to 60nm and may or may not be doped with a p-type species such as Mg.

In a specific preferred embodiment, an AlGaN electron blocking layer,with an aluminum content of between 5% and 20% (mole percent), ispositioned between the MQW and the p-type GaN cladding layer eitherbetween the MQW and the p-side SCH, within the p-side SCH, or betweenthe p-side SCH and the p-type GaN cladding. The AlGaN electron blockinglayer ranges in thickness from 5 nm to 20 nm and is doped with a p-typedopant such as Mg from 1E17 cm⁻³ and 1E21 cm⁻³ according to a specificembodiment. In other embodiments, the electron blocking layer is freefrom any aluminum species and/or may be eliminated all together. In yetanother embodiment, the device may be substantially free from anelectron blocking layer.

Preferably, a p-contact layer positioned on top of and is formedoverlying the p-type cladding layer. The p-contact layer may compriseGaN doped with a p-dopant such as Mg at a level ranging from 1E20 cm⁻³to 1E22 cm⁻³.

In an example, a laser device has a gallium and nitrogen containingsubstrate member (e.g., bulk gallium nitride) having a {20-21}crystalline surface region or other surface configuration. The devicehas an n-type gallium and nitrogen containing cladding material. In aspecific embodiment, the n-type gallium and nitrogen containing claddingmaterial is substantially free from an aluminum species, which leads toimperfections, impurities, and other limitations. In one or morepreferred embodiment, the cladding material has no aluminum species andis made of a gallium and nitrogen containing material.

In a specific embodiment, the device also has an active region includingmultiple quantum well structures overlying the n-type gallium andnitrogen containing cladding material. In one or more embodiments, theactive regions can include those noted, as well as others. That is, thedevice can include InGaN/InGaN and/or InGaN/GaN active regions, amongothers. In a specific embodiment, the optical can include seven MQW, sixMQW, five MQW, four MQW, three MQW, more MQW, or fewer, and the like.

In a specific embodiment, the device has a p-type gallium and nitrogencontaining cladding material overlying the active region. In a preferredembodiment, the p-type gallium and nitrogen containing cladding materialis substantially free from an aluminum species, which leads toimperfections, defects, and other limitations. In one or more preferredembodiment, the cladding material has no aluminum species and is made ofa gallium and nitrogen containing material.

In a specific embodiment, the device preferably includes a laser striperegion configured from at least the active region and characterized by acavity orientation substantially parallel to a projection in ac-direction. Other configurations may also exist depending upon thespecific embodiment. The laser strip region has a first end and a secondend or other configurations. In a specific embodiment, the device alsohas a first etched facet provided on the first end of the laser striperegion and a second etched facet provided on the second end of the laserstripe region.

In yet other embodiments, the present device includes a gallium andnitrogen containing electron blocking region that is substantially freefrom aluminum species. In yet other embodiments, the device does notinclude any electron blocking layer or yet in other embodiments, thereis no aluminum in the cladding layers and/or electron blocking layer.

In preferred embodiments, the present method and structure issubstantially free from InAlGaN or aluminum bearing species in thecladding layers as conventional techniques, such as those in Yoshizumiet al., “Continuous-Wave operation of 520 nm Green InGaN-Based LaserDiodes on Semi-Polar {20-21} GaN Substrates,” Applied Physics Express 2(2009) 092101. That is, the present laser structure and method aresubstantially free from any aluminum species in the cladding region.Aluminum is generally detrimental. Aluminum often leads to introductionof oxygen in the reactor, which can act as non radiative recombinationcenters to reduce the radiative efficiency and introduce otherlimitations. We also determined that oxygen can compensate p-typedopants in the p-cladding to cause additional resistivity in the opticaldevice. In other aspects, we also determined that aluminum isdetrimental to the MOCVD reactor and can react or pre-react with othergrowth precursors. Use of aluminum cladding layers is also cumbersomeand can take additional time to grow. Accordingly, it is believed thatthe aluminum cladding free laser method and structure are generally moreefficient to grow than conventional laser structures. Further details ofthe present laser configured on {20-21} is disclosed in U.S. applicationSer. No. 12/883,652 filed on Sep. 16, 2010, which is incorporated byreference in its entirety.

In an example, a gallium and nitrogen containing laser device configuredon either a nonpolar or a semipolar surface orientation. The device hasa gallium and nitrogen containing substrate member and a cladding regionoverlying the substrate member. In an example, the device has a cavityregion formed overlying the cladding region and configured in alignmentin substantially a c-direction or a projection of the c-direction.Preferably, a cavity region is characterized by a first end and a secondend. In an example, the device has a first optical coating formedoverlying the first facet, wherein the first coating overlying the firstfacet is configured to increase a reflectivity and a second opticalcoating formed overlying the second facet, wherein the second coatinglayer overlying the second facet is configured to reduce a reflectivity.The device has an optical power density characterizing the laser device,the laser device being substantially free from COMD related failure.

In an example, the nonpolar or semipolar surface orientation comprisesan m-plane, a (30-31) plane, a (20-21) plane, a (30-32) plane, a(30-3-1) plane, a (20-2-1) plane, a (30-3-2) plane, or an offcut ofwithin +/−5 degrees of any of these planes toward an a-direction or ac-direction; the cladding region being substantially free fromAl-containing material, the cladding region being characterized by anAlN mol fraction in the cladding region of less than about 2%. In anexample, the first optical coating is provided by a method selected fromelectron-beam deposition, thermal evaporation, PECVD, sputtering, and acombination of any of the foregoing. In other examples, the presentinvention also includes related methods reciting the same or similarelements.

In an example, the device comprises an output cavity width of greaterthan about 3 μm and less than about 25 μm, and is operable at over 1 Wor wherein the device comprises an output cavity width of greater thanabout 3 μm and less than about 25 μm and is operable at over 2 W orwherein the device comprises an output cavity width of greater thanabout 3 μm and less than about 35 μm, and is operable at over 3 W orwherein the device comprises an output cavity width of greater thanabout 3 μm and less than about 35 μm, and is operable at over 4.5 W orwherein the device comprises an output cavity width of greater thanabout 3 μm and less than about 50 μm and is operable at over 3 W. In anexample, the device is substantially free from COMD for power levelsgreater than 100 mW per micron of output cavity width, 200 mW per micronof output cavity width, or 400 mW per micron of output cavity width.

The method and device here can be configured with conductive oxides, lowtemperature p-clad, n-contact scribes, beam clean-up scribes, amongothers. It can also include an indium tin oxide (ITO) or ZnO claddingregion on top of a thin p-type layer such as p-GaN layer or region of200 A to 2000 A for laser diodes or LEDs. Certain GaN planes may sufferfrom severe thermal degradation in the active region during growth ofthe electron blocking layer and the p-cladding layers where elevatedtemperatures are used. In a preferred embodiment, if ZnO or ITO isformed in place of a portion or substantially the p-clad layer orregion, desirable p-type material can be achieved without subjecting theresulting device to a long growth time of the p-layer. That is, afterthe epitaxial growth is completed by MOCVD or other method such as MBE,one or more conducting oxide layers such as indium-tin-oxide (ITO) orzinc oxide (ZnO) may then be deposited directly on or generally abovethe thin p-cladding layer. These conducting oxide layers can bedeposited at a temperature lower than a typical p-cladding growthtemperature and even substantially lower than the growth temperature ofthe light emission region. This will prevent or drastically reduce anythermal degradation to the light emission region that may have occurredduring the epitaxial growth of the conventional p-cladding region. Theresulting conducting oxide layer can act as a p-cladding region in bothlaser and LED structures and can enable the formation of a goodp-contact on top of the conducting oxide layer that results in ohmic orquasi-ohmic characteristics. Additionally, the conducting oxide layerscan have optical absorption coefficients in the blue and greenwavelength ranges of interest that are lower or significantly lower thanthe optical absorption coefficient of a typical highly doped epitaxialp-type cladding regions such as GaN or AlGaN, and may therefore help toreduce optical absorption for lower internal losses in a laser cavity orhigher extraction efficiency in an LED device. In an alternativeembodiment, metallic layers such as silver may be used in place ofconducting oxide layers.

In a specific embodiment, the method and device can also include growthof a very low temperature p-cladding on top of the quantum well or lightemitting layers. By developing epitaxial conditions that enable lowresistance p-cladding sufficient for good device performance with agrowth temperature of 700° C. to 800° C., 800° C. to 850° C., or 850° C.to 875° C. degradation to the quantum well or light emitting regions canbe reduced.

In another embodiment using a transparent conductive oxide such as ITOthe transparent conductive oxide maybe deposited above p-type claddingregion(s) and below metallization layers. The conductive oxide such asITO may serve as a low refractive index layer to reduce the amount ofmodal overlap with the overlying metallization layers, and hence reducethe internal loss of the laser diode. Such a reduction of internal lossmay increase the efficiency of the laser device. There are many methodsand processes to form the conductive oxide layer including depositing itwith an ebeam technique, a sputter technique, an evaporation technique,or with an electron cyclotron resonance (ECR) technique. The conductiveoxide may be deposited only on top of the laser stripe or the conductiveoxide may be deposited over a larger area so that it extends laterallyfrom the top of the laser stripe. Metallization of conventional metalssuch as Au, Pd, Ni, Pt, and Ti may then be performed overlying a regionof the conductive oxide.

In another embodiment to reduce internal loss of a laser by mitigatingthe modal overlap with the metal regions overlying the p-type cladding,a highly reflective metal such as Ag can be deposited between the p-typegallium and nitrogen cladding region and the primary metallizationlayers. The reflective metal layer(s) such as silver may serve toreflect the electromagnetic radiation from the optical mode and reducethe modal overlap with the overlying metallization layers, and hencereduce the internal loss of the laser diode. Such a reduction ofinternal loss may increase the efficiency of the laser device. There aremany methods and processes to form the highly reflective metal layerincluding depositing it with an ebeam technique, a sputter technique, oran evaporation technique. The reflective metal layer may be depositedonly on top of the laser stripe or the reflective metal layer may bedeposited over a larger area so that it extends laterally from the topof the laser stripe. Metallization of conventional metals such as Au,Pd, Ni, Pt, and Ti may then be performed overlying a region of thehighly reflective metal layers.

In a specific embodiment on the {20-2-1} GaN, the device has a laserstripe region formed overlying a portion of the off-cut crystallineorientation surface region. The laser stripe region is characterized bya cavity orientation substantially in a projection of a c-direction,which is substantially normal to an a-direction. The laser stripe regionhas a first end 807 and a second end 809 and is formed on a projectionof a c-direction on a {20-2-1} gallium and nitrogen containing substratehaving a pair of cleaved mirror structures which face each other. Thecleaved facets provide a reflective coating, no coating, anantireflective coating, or expose gallium and nitrogen containingmaterial.

In embodiments, the device has a first cleaved facet provided on thefirst end of the laser stripe region and a second cleaved facet providedon the second end of the laser stripe region. The first cleaved facet issubstantially parallel with the second cleaved facet. Mirror surfacesare formed on each of the cleaved surfaces. The mirror surface of thefirst cleaved facet is provided by a top-side skip-scribe scribing andbreaking process. The scribing process can use any suitable techniques,such as a diamond scribe or laser scribe. In a specific embodiment, thefirst mirror surface comprises a reflective coating. The reflectivecoating is selected from silicon dioxide, hafnia, and titania, tantalumpentoxide, zirconia, or combinations thereof. Depending upon theembodiment, the first mirror surface can also comprise ananti-reflective coating.

Also, in certain embodiments, the second cleaved facet comprises asecond mirror surface provided by a top side skip-scribe scribing andbreaking process. Preferably, the scribing is diamond scribed or laserscribed. In a specific embodiment, the second mirror surface comprises areflective coating, such as silicon dioxide, hafnia, and titania,tantalum pentoxide, zirconia, combinations, and the like.

In certain embodiments, the device has a first cleaved facet provided onthe first end of the laser stripe region and a second cleaved facetprovided on the second end of the laser stripe region. The first cleavedfacet is substantially parallel with the second cleaved facet. Mirrorsurfaces are formed on each of the cleaved surfaces. The mirror surfaceof the first cleaved facet is provided by a nicking and breaking processwhere a nick is induced in the semiconductor material using a laserscribe or diamond scribe. This nick behaves as a crack initiation sitesuch that during the breaking process a crack is induced and propagatesa cleavage place to form a cleaved facet. Guiding etches or scribes maybe used to guide the cleavage plane along a predetermined direction. Thenick scribing process can use any suitable techniques, such as a diamondscribe or laser scribe. In a specific embodiment, the first mirrorsurface comprises a reflective coating. The reflective coating isselected from silicon dioxide, hafnia, and titania, tantalum pentoxide,zirconia, or combinations thereof. Depending upon the embodiment, thefirst mirror surface can also comprise an anti-reflective coating.

Also, in certain embodiments, the second cleaved facet comprises asecond mirror surface provided by a nicking and breaking process where anick is induced in the semiconductor material using a laser scribe ordiamond scribe. The nick behaves as a crack initiation site such thatduring the breaking process a crack is induced and propagates a cleavageplace to form a cleaved facet. Guiding etches or scribes may be used toguide the cleavage plane along a predetermined direction. The nickscribing process can use any suitable techniques, such as a diamondscribe or laser scribe. In a specific embodiment, the second mirrorsurface comprises a reflective coating, such as silicon dioxide, hafnia,and titania, tantalum pentoxide, zirconia, combinations, and the like.

In certain embodiments, the device has a first etched facet provided onthe first end of the laser stripe region and a second etched facetprovided on the second end of the laser stripe region. The first etchedfacet is substantially parallel with the second etched facet. Mirrorsurfaces are formed on each of the etched surfaces. The mirror surfaceof the first etched facet is provided by a lithography and etchingprocess where the etching process is selected from one of the followingof chemical assisted ion beam etching (CABE), reactive ion etching(RIE), or inductively coupled plasma (ICP) etches. In a specificembodiment, the first mirror surface comprises a reflective coating. Thereflective coating is selected from silicon dioxide, hafnia, andtitania, tantalum pentoxide, zirconia, or combinations thereof.Depending upon the embodiment, the first mirror surface can alsocomprise an anti-reflective coating.

Also, in certain embodiments, the second etched facet comprises a secondmirror surface provided by a lithography and etching process alithography and etching process where the etching process is selectedfrom one of the following of chemical assisted ion beam etching (CAIBE),reactive ion etching (RIE), or inductively coupled plasma (ICP) etches.In a specific embodiment, the second mirror surface comprises areflective coating, such as silicon dioxide, hafnia, and titania,tantalum pentoxide, zirconia, combinations, and the like.

The laser stripe has a length from about 50 microns to about 3000microns, but is preferably between 50 microns and 300 microns, 300microns and 900 microns, or 900 microns and 1600 microns. The stripealso has a width ranging from about 0.5 microns to about 50 microns, butis preferably between 0.8 microns and 3 microns or between 3 microns andabout 35 microns. In a specific embodiment, the overall device has awidth ranging from about 0.5 microns to about 15.0 microns. In aspecific embodiment, the width is substantially constant in dimension,although there may be slight variations. The width and length are oftenformed using a masking and etching process, which are commonly used inthe art.

This invention provides an optical device structure capable of emitting501 nm and greater (e.g., 525 nm) light in a ridge laser embodiment. Thedevice preferably includes: (1) a gallium and nitrogen containingsubstrate configured with a {20-2-1} surface region, (2) an InGaNseparate confinement heterostructure, (3) a gallium nitrogen barrierlayer(s), (4) a plurality of InGaN quantum wells (2 to 10), (5) agallium nitrogen barrier layer(s), (6) an AlGaN electron blocking layer,(7) a p-type gallium nitrogen cladding layer, and (8) a p+ galliumnitrogen contact layer.

In an example, the present method and structure has trenches each ofwhich is 5-10 microns wide, although there can be variations, e.g., 1micron or narrower trenches may still be able to block trenches. In anexample, wider trenches may be configured as long as they do notinterference with useful area for device fabrication. As each of thetrenches become wide, like wider than 25 microns to 50 microns, theresulting structure actually becomes more like a mesa structure wherethere is more trench region than an elevated region such that the devicemay actually appear on a mesa as opposed to just having trenchesprotecting it, although there can be variations. With that said, mesastructures are desirable and are not excluded. In an example, trenchregions can be greater than 0.1 microns, greater than 0.5 microns,greater than 1 micron, and greater than 3 microns.

In an example, as for the growth regions (e.g., the whole wafer is agrowth region), each of these will range from 5 microns wide to 50microns or 200 microns wide, including variations. In an example,smaller growth regions are desirable since they can lead to fewerdefects, although they growth region should be large enough to form alaser device thereon and achieve smooth epi close to these interfaces onthe boundary of the trenches. In an example, desirable trench width willbe in the 10 to 50 microns, among others.

In an example, a ratio defined between spatial regions of the trenchesto growth regions can vary. In an example, a mesa structure to growthregion can have a ratio of 5% and greater and a narrow trench structureto growth region can have a ratio up to 95%, although there can bevariations.

In an example, one of the benefits of the present method and structureis reduced misfit dislocations as described. For a given epi structurewith high strain the number of misfit dislocations is greatly reduced inthese regions depending on the width of the region. In an example, thereduced dislocations also lead to resulting higher strained structures.That is, the method and structure achieves growth structures with muchhigher strain and still maintain good film quality. In an example,growth structures with 7, 9, or 11 quantum wells can be formed, whilestill maintaining good epi quality. In other embodiments, SCH regionswith much higher indium content for better confinement are achieved,while still maintaining a high film quality.

In an example, it has been discovered that certain semipolar planes aremore susceptible to thermal degradation of the light emitting activeregion during the subsequent growth of the p-type layers above theactive region such as electron blocking layers, p-cladding layers, andp-contact layers. This thermal degradation characteristic results inreduced brightness or optical output power from the light emittingregion using photoluminescence or electroluminescence measurements. Thereduced brightness indicates reduced internal efficiency of the materialdue to the introduction of defects that act as non-radiativerecombination centers. Such non-radiative recombination centersultimately reduce device efficiency and can even prevent laser diodeoperation.

In an embodiment for lasers fabricated on a family of planes including,but not limited to, (30-3-2), (20-2-1), (30-3-1), (30-32), (20-21),(30-31) or any orientation within +/−10 degrees toward c-plane and/ora-plane from these orientations, the epitaxial device structure maycontain a thin, 5 nm to 20 nm, 20 nm to 100 nm, 100 nm to 300 nm p-typeregion grown above the light emitting or quantum well regions. This thinp-type layer or layers may be characterized by a p-type cladding layer,an electron blocking layer, some combination, or other and may compriseGaN, AlGaN, InGaN, or InAlGaN and doped with a p-type species such asmagnesium. Ultra-thin layers in this range grown at temperatures below,about equal to, or only slightly hotter (10° C. to 75° C.) than thegrowth temperature used for the light emitting layers can mitigate thethermal degradation to the light emitting layers that occurs when thelayers are grown hotter or thicker. The reduced thermal degradation is aresult of the relatively short growth time and the low growthtemperature required for deposition of the thin p-clad layer.

After the epitaxial growth is completed by MOCVD or other method such asMBE, one or more conducting oxide layers such as indium-tin-oxide (ITO)or zinc oxide (ZnO) may then be deposited directly on or generally abovethe thin p-cladding layer. These conducting oxide layers can bedeposited at a temperature lower than a typical p-cladding growthtemperature and even substantially lower than the growth temperature ofthe light emission region. This will prevent or drastically reduce anythermal degradation to the light emission region that may have occurredduring the epitaxial growth of the conventional p-cladding region. Theresulting conducting oxide layer can act as a p-cladding region in laserstructures and can enable the formation of a good p-contact on top ofthe conducting oxide layer that results in ohmic or quasi-ohmiccharacteristics. Additionally, the conducting oxide layers can haveoptical absorption coefficients in the blue and green wavelength rangesof interest that are lower or significantly lower than the opticalabsorption coefficient of a typical highly doped epitaxial p-typecladding regions such as GaN or AlGaN, and may therefore help to reduceoptical absorption for lower internal losses in a laser cavity. In analternative embodiment, metallic layers such as silver may be used inplace of conducting oxide layers.

In another embodiment for lasers fabricated on a family of planesincluding, but not limited to, (30-3-2), (20-2-1), (30-3-1), (30-32),(20-21), (30-31) or any orientation within +/−10 degrees toward c-planeand/or a-plane from these orientations, the epitaxial device structuremay contain a p-type cladding region grown at very low growthtemperature while still enabling an acceptable voltage characteristicwithin the device. The p-cladding layer may comprise GaN, AlGaN, InGaN,or InAlGaN and may be doped with a species such as magnesium. The verylow growth temperature may be less than, equal to, or only slightlyhigher (10° C. to 50° C.) than the growth temperature used for the lightemitting layers. More typically, the p-cladding region is grown attemperatures more than 50° C., more than 100° C., or more than 150° C.hotter than the light emitting layers. The substantially lower growthtemperature may mitigate degradation to the light emitting layers thattypically occurs when the layers are grown hotter or thicker. In a laserdiode structure, the growth conditions, layer thickness, and layercomposition may be designed to enable a laser device operable below 7V,operable below 6V, or operable below 5V.

An example of a laser diode with a conductive oxide layer that comprisesa substantial portion of the p-type cladding region is included. In thisembodiment the waveguide stripe region is comprised entirely of theconductive oxide such that it forms all of the lateral index contrast toprovide the lateral waveguide. As an example, the conductive oxide canbe an indium tin oxide, or other suitable material.

An example of a laser diode with a conductive oxide layer that comprisesa substantial portion of the p-type cladding region is included. In thisembodiment the waveguide stripe region comprises a combination of aconductive and an epitaxially deposited p-type material such as p-typeGaN, AlGaN, InAlGaN, or other gallium and nitrogen containing materials.In this embodiment the conductive oxide and the epitaxially formedp-type material provides the lateral index contrast to provide thelateral waveguide.

An example process flow for forming a laser diode with a conductiveoxide layer that comprises a substantial portion of the p-type claddingregion is included. In this example the epitaxially grown wafer issubjected to a photolithography process that may result in openings inthe photoresist where the desired lasers stripes will be positioned.Following the photolithography the conductive oxide layer is depositedon the patterned wafer. The deposition methods include sputtering,electron beam, electron cyclotron resonance (ECR) deposition, or variousother evaporation methods. The ECR deposition occurs at a rate of 1-3angstroms per second, provides an ohmic contact to the p-layer it isdeposited on, and provides a suitable sheet resistance for andabsorption coefficient for forming an electrically conductive and lowoptical loss cladding region. This is followed by a lift-off processwhere the conductive oxide on top of the photoresist is removed from thewafer to result in laser stripe regions defined by the remainingconductive oxide stripes. In this embodiment the conductive oxide striperegion forms all of the lateral index contrast to provide the lateralwaveguide.

An alternative example process flow for forming a laser diode with aconductive oxide layer that comprises a substantial portion of thep-type cladding region is included. In this example the epitaxiallygrown wafer is subjected to a blanket deposition of a conductive oxidelayer. The deposition methods include sputtering, electron beam,electron cyclotron resonance (ECR) deposition, or various otherevaporation methods. Following the deposition a photolithography processis used to define laser stripe patterns in the photoresist where thedesired lasers stripes will be positioned. Following thephotolithography step and etching process is carried out to remove theconductive oxide layer in the field without the photoresist. Thisetching process can be wet or dry. An example of a wet etch chemistrymay include HCl or HCl and FeCl₃. In this embodiment the conductiveoxide stripe region forms all of the lateral index contrast to providethe lateral waveguide.

In another embodiment using a transparent conductive oxide such as ITOthe transparent conductive oxide may be deposited above p-type claddingregion(s) and below metallization layers. In this embodiment thetransparent conductive oxide may or may not form a substantial portionof the p-type cladding region and may primarily serve as a lowrefractive index layer to reduce the amount of modal overlap with theoverlying metallization layers which are very lossy/absorbing to theoptical mode of the laser diode. Such a configuration may substantiallyprevent the optical mode from overlapping the metal and hence reduce theinternal loss of the laser diode. Such a reduction of internal loss mayincrease the efficiency of the laser device. In a preferred process,after the ridge was formed using a wet or dry etching process to definethe laser stripe and the dielectric passivation layer was deposited topassivate the regions surrounding the top of the ridge, but leaving anopening on the top of the ridge exposing a semiconductor surface, aconductive oxide may be deposited on top of the exposed semiconductorregion on top of the ridge and may also overly some of the surroundingdielectric passivation region. The conductive oxide may then bepatterned through a lift off process or by a wet or dry etching process.Metallization layers such as Au, Pd, Ni, Pt, and Ti may then beperformed overlying a region of the conductive oxide. There are manymethods and processes to form the conductive oxide layer includingdepositing it with an ebeam technique, a sputter technique, anevaporation technique, or with an electron cyclotron resonance (ECR)technique.

In another embodiment to reduce loss from the metallization layersoverlying the p-type cladding regions a highly reflective metal such assilver may be deposited above p-type cladding region(s) and below theprimary metallization layers. In this embodiment the highly reflectivemetal may primarily serve as a reflector layer to reduce the amount ofmodal overlap with the overlying metallization layers, and hence reducethe internal loss of the laser diode. Such a reduction of internal lossmay increase the efficiency of the laser device. In a preferred process,after the ridge was formed for the laser diode and the dielectricpassivation layer was deposited to passivate the regions surrounding thetop of the ridge, but leaving an opening on the top of the ridgeexposing a semiconductor surface, a highly reflective metal layer suchas Ag may be deposited on top of the exposed semiconductor region on topof the ridge and may also overly some of the surrounding dielectricpassivation region. The highly reflective metal layer such as silver maythen be patterned through a lift off process or by a wet or dry etchingprocess. Metallization layers such as Au, Pd, Ni, Pt, and Ti may then beperformed overlying a region of the conductive oxide. Further, in oneembodiment, Pt or another metal may be added to the highly reflectivelayer to improve characteristics such as the contact resistance to thesemiconductor surface. There are many methods and processes to form theconductive oxide layer including depositing it with an ebeam technique,a sputter technique, or with an evaporation technique.

In one preferred embodiment an electron cyclotron resonance (ECR)deposition method is used to form an indium tin oxide (ITO) layer as theelectrically conductive oxide. By using the ECR process to deposit ITO alow damage will be inflicted on the semiconductor surface to enable verygood contact resistance. The bulk resistivity of these ITO films can beless than about 10E⁻⁴ ohm-cm, less than about 4E⁻⁴ ohm-cm, or less thanabout 3E⁻⁴ ohm-cm. This resistivity is drastically higher than typicalp-type GaN or p-type AlGaN which can be 3-4 orders of magnitude higher.The lower resistivity will result in a lower device series resistanceand hence a lower operating voltage within the laser diode for higherefficiency. Further, the index of refraction of the ITO will be lowerthan that of GaN, AlGaN, or InAlGaN to provide better waveguiding forlaser diodes operating in the blue and green wavelength regimes. Forexample, in the 450 nm range the index of refraction for ITO is about2.05 and for GaN it is about 2.48 while in the 525 nm range the index ofrefraction for ITO is about 1.95 and for GaN it is about 2.41. The lowerindex of the ITO will provide higher index contrast with the InGaN basedactive region and hence can provide higher overlap with the quantumwells for higher modal gain. In a specific example, the conductive oxideis formed at a temperature lower than 350° C. or lower than 200° C.Additionally, for both the conductive oxide and the low temp pGaN, thelaser device is operable in the 500 nm to 600 nm range.

In an alternative embodiment an electron cyclotron resonance (ECR)deposition method is used to form a zinc oxide (ZnO) layer as theelectrically conductive oxide. By using the ECR process to deposit ZnO alow damage will be inflicted on the semiconductor surface to enable verygood contact resistance. The ECR deposition occurs at a rate of 1-3angstroms per second, provides an ohmic contact to the p-layer it isdeposited on, and provides a suitable sheet resistance for andabsorption coefficient for forming an electrically conductive and lowoptical loss cladding region.

In yet an another preferred embodiment, the transparent conductive oxidesuch as ITO is deposited through a low damage sputtering process. Insuch a process it is very important that the sputtering process doesinflict damage to the semiconductor layer and create a very high contactresistance. As used herein, the term GaN substrate is associated withGroup III-nitride based materials including GaN, InGaN, AlGaN, or otherGroup III containing alloys or compositions that are used as startingmaterials. Such starting materials include polar GaN substrates (i.e.,substrate where the largest area surface is nominally an (h k 1) planewherein h=k=0, and 1 is non-zero), non-polar GaN substrates (i.e.,substrate material where the largest area surface is oriented at anangle ranging from about 80-100 degrees from the polar orientationdescribed above toward an (h k l) plane wherein l=0, and at least one ofh and k is non-zero) or semi-polar GaN substrates (i.e., substratematerial where the largest area surface is oriented at an angle rangingfrom about +0.1 to 80 degrees or 110-179.9 degrees from the polarorientation described above toward an (h k l) plane wherein l=0, and atleast one of h and k is non-zero).

As shown, the present device can be enclosed in a suitable package. Suchpackage can include those such as in TO-38 and TO-56 headers. Othersuitable package designs and methods can also exist, such as TO-9 orflat packs where fiber optic coupling is required and even non-standardpackaging. In a specific embodiment, the present device can beimplemented in a co-packaging configuration such as those described inU.S. Application Publication No. 2010/0302464, which is incorporated byreference in its entirety.

In other embodiments, the present laser device can be configured in avariety of applications. Such applications include laser displays,metrology, communications, health care and surgery, informationtechnology, and others. As an example, the present laser device can beprovided in a laser display such as those described in U.S. ApplicationPublication No. 2010/0302464, which is incorporated by reference in itsentirety.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. As an example, the packaged device can include any combination ofelements described above, as well as outside of the presentspecification. As used herein, the term “substrate” can mean the bulksubstrate or can include overlying growth structures such as a galliumand nitrogen containing epitaxial region, or functional regions such asn-type GaN, combinations, and the like. Additionally, the examplesillustrates two waveguide structures in normal configurations, there canbe variations, e.g., other angles and polarizations. For semi-polar, thepresent method and structure includes a stripe oriented perpendicular tothe c-axis, an in-plane polarized mode is not an Eigen-mode of thewaveguide. The polarization rotates to elliptic (if the crystal angle isnot exactly 45 degrees, in that special case the polarization may rotatebut be linear, like in a half-wave plate). The polarization will ofcourse not rotate toward the propagation direction, which has nointeraction with the Al band. The length of the a-axis stripe determineswhich polarization comes out at the next mirror.

Although the embodiments above have been described in terms of a laserdiode, the methods and device structures can also be applied to anylight emitting diode device. Therefore, the above description andillustrations should not be taken as limiting the scope of the presentinvention which is defined by the appended claims.

What is claimed is:
 1. A gallium and nitrogen containing laser diodedevice, the device comprising: a gallium and nitrogen containingsubstrate material comprising a surface region; a plurality of recessedregions within the substrate material, each pair of adjacent recessedregions forming a mesa region therebetween, the mesa region having awidth of at least 0.5 microns, the pair of adjacent recessed regionsbeing configured to block a plurality of defects from migrating into themesa region; an epitaxial gallium and nitrogen containing materialoverlying the substrate material and the mesa region, the epitaxialgallium and nitrogen containing material overlying the mesa region beingsubstantially free from defects migrating from regions outside the pairof adjacent recessed regions to the mesa region; an active regionoverlying the epitaxial gallium and nitrogen containing material,wherein the epitaxial gallium and nitrogen containing material and theactive region overlie sidewalls and bottoms of the plurality of recessesregions; a p-type region overlying the active region, wherein a topsurface of a portion of the epitaxial gallium and nitrogen containingmaterial that extends over the bottoms of at least some of the pluralityof recessed regions is below a top surface of the surface region so thatthe epitaxial gallium and nitrogen containing material does notcompletely fill at least some of the plurality of recessed regions, anda top surface of a portion of the p-type region that extends over thebottoms of the plurality of recessed regions is substantially planar andcoalesces to fill depressions above the plurality of recessed regions; alaser stripe region overlying at least a portion of the mesa region, thelaser stripe region having a first end and a second end; and a firstfacet provided on the first end of the laser stripe region and a secondfacet provided on the second end of the laser stripe region.
 2. Thedevice of claim 1, further comprising a p-type cladding regioncomprising an (InAl)GaN material doped with a plurality of magnesiumspecies formed overlying the active region.
 3. The device of claim 1,wherein the surface region has an orientation selected from one of{30-3-1}, {30-31}, {20-2-1}, {30-3-2}, {20-21}, {30-3-1}, {30-32}, or anoffcut from any one of these planes within +/−5 degrees toward ac-plane.
 4. The device of claim 1, wherein the active region comprisesInGaN quantum wells configured to emit in the blue range having awavelength of between 430 nm to 480 nm or in the green range having awavelength of between 500 nm to 540 nm.
 5. The device of claim 1,wherein the p-type region is a p-type gallium and nitrogen containingcladding region, and the device comprises: a conductive oxide layercomprising an indium tin oxide overlying the p-type gallium and nitrogencontaining cladding region; and a metallization layer selected from atleast one of Au, Ni, Pd, Pt, or Ti overlying the conductive oxide layer.6. The device of claim 1, wherein the p-type region is a p-type galliumand nitrogen containing cladding region, and the device comprises: ahighly reflective metal layer overlying the p-type gallium and nitrogencontaining cladding region; and a metallization layer selected from atleast one of Au, Ni, Pd, Pt, or Ti overlying the highly reflective metallayer.
 7. The device of claim 1, wherein, the active region comprisesone or more light emitting layers; each of the one or more lightingemitting layers being configured between a pair of barrier regions; eachof the one or more lighting emitting layers having a thickness rangingfrom about 2 nm to about 8 nm; and each of the barrier regions having athickness ranging from 2 nm to 4 nm or 4 nm to 8 nm or 8 nm to 20 nm. 8.The device of claim 1, wherein the epitaxial gallium and nitrogenmaterial comprises a defect density of less than 10⁵ cm⁻²; wherein eachrecessed region comprises a width ranging from 5 microns to 200 microns;and wherein the gallium and nitrogen containing substrate material isGaN.
 9. The device of claim 1, wherein the first and second facets arecleaved facets.
 10. The device of claim 1, wherein the first and secondfacets are etched facets.
 11. A structure for a gallium and nitrogencontaining laser diode device, the structure comprising: a gallium andnitrogen containing substrate material comprising a surface region; aplurality of migration blocking regions (MBRs) within the substratematerial, each of the MBRs including a recessed region, and each pair ofadjacent MBRs forming a mesa region therebetween, the mesa region havinga width of at least 0.5 microns, the pair of adjacent MBRs beingconfigured to block a plurality of defects from migrating into the mesaregion; an epitaxial gallium and nitrogen containing material overlyingthe substrate material, the epitaxial gallium and nitrogen containingmaterial overlying the mesa region being substantially free from defectsmigrating from regions outside the pair of adjacent MBRs to the mesaregion; an active region overlying the epitaxial gallium and nitrogencontaining material and the mesa region, wherein the epitaxial galliumand nitrogen containing material and the active region overlie sidewallsand bottoms of the plurality of MBRs; and a p-type region overlying theactive region, wherein a top surface of a portion of the epitaxialgallium and nitrogen containing material that extends over the bottomsof at least some of the plurality of MBRs is below a top surface of thesurface region so that the epitaxial gallium and nitrogen containingmaterial does not completely fill at least some of the plurality ofMBRs, and a top surface of a portion of the p-type region that extendsover the bottoms of the plurality of MBRs is substantially planar andcoalesces to fill depressions above the plurality of MBRs.
 12. Thestructure of claim 11, wherein the plurality of MBRs are provided by atrench, a mesa, or another structure or patterned mask.
 13. Thestructure of claim 11, wherein the plurality of MBRs are provided by anetched mesa using a patterned mask.
 14. The structure of claim 11,wherein the plurality of MBRs are provided by a deposited and patternedmaterial comprising at least one of silicon dioxide or silicon nitride.15. The structure of claim 11, further comprising a laser stripe regionoverlying the p-type region.
 16. The structure of claim 11, furthercomprising a laser stripe region overlying the p-type region, whereinthe laser stripe region is characterized by a cavity orientationsubstantially parallel to a projection of a c-direction; the laserstripe region having a first end and a second end; a first facetprovided on the first end of the laser stripe region and a second facetprovided on the second end of the laser stripe region.
 17. The structureof claim 16, wherein the first facet and the second facet are etchedfacets; or where in the first facet and the second facet are cleavedfacets.
 18. The structure of claim 11, wherein the p-type region is ap-type cladding region comprising an (InAl)GaN material doped with aplurality of magnesium species; wherein the surface region has anorientation selected from one of {30-3-1}, {30-31}, {20-2-1}, {20-21},{30-3-1}, {30-32}, or an offcut from any one of these planes within +/−5degrees toward a c-plane.
 19. A method for fabricating a gallium andnitrogen containing laser diode device, the method comprising: providinga gallium and nitrogen containing substrate material comprising asurface region; forming a plurality of migration blocking regions (MBRs)within the substrate material, each of the MBRs including a recessedregion, and each pair of adjacent MBRs forming a mesa regiontherebetween, the mesa region having a width of at least 0.5 microns,the pair of adjacent MBRs being configured to block a plurality ofdefects from migrating into the mesa region; forming an epitaxialgallium and nitrogen containing material overlying the substratematerial, the epitaxial gallium and nitrogen containing materialoverlying the mesa region being substantially free from defectsmigrating from regions outside the pair of adjacent MBRs to the mesaregion; forming an active region overlying the epitaxial gallium andnitrogen containing material and the mesa region, wherein the epitaxialgallium and nitrogen containing material and the active region overliesidewalls and bottoms of the plurality of MBRs; and forming a p-typeregion overlying the active region, wherein a top surface of a portionof the epitaxial gallium and nitrogen containing material that extendsover the bottoms of at least some of the plurality of MBRs is below atop surface of the surface region so that the epitaxial gallium andnitrogen containing material does not completely fill at least some ofthe plurality of MBRs, and a top surface of a portion of the p-typeregion that extends over the bottoms of the plurality of MBRs issubstantially planar, the p-type region coalescing to fill depressionsabove the plurality of MBRs.